UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 


COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 


BERKELEY,  CALIFORNIA 


THE  BLACK  SCALE 


By  H.  J.  QUAYLE 
Assisted  by  E.  W.  RUST 


X 


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J 


BULLETIN  No.  223. 

BERKELEY,    CAL.,    JULY,    1911 


W.    W.    SHANNON 


SACRAMENTO 

SUPERINTENDENT    STATE    PRINTING 
1911 


Benjamin  Ide  Wheeler,  President  of  the  University. 

EXPERIMENT  STATION  STAFF. 


E.  J.  Wickson,  M.A.,  Director  and  Horticulturist. 

E.  W.  Hilgard,  Ph.D.,  LL.D,  Chemist  (Emeritus). 

W.  A.  Setchell,  Ph.D.,  Botanist. 

Leroy  Anderson,  Ph.D.,  Dairy  Industry  and  Superintendent  University  Farm  Schools 

M.  E.  Jaffa,  M.S.,  Nutrition  Expert. 

R.  H.  Loughridge,  Ph.D.,   Soil  Chemist  and  Physicist   (Emeritus). 

C.  W.  Woodworth,  M.S.,  Entomologist. 

Ralph  E.  Smith,  B.S.,   Plant  Pathologist  and  Superintendent  of  Southern  California 

Pathological  Laboratory  and  Experiment  Station. 
G.  W.  Shaw,  M.A.,  Ph.D.,  Experimental  Agronomist  and  Agricultural  Technologist,  in 

charge  of  Cereal  Stations. 
E.  W.  Major,  B.Agr.,  Animal  Industry. 

B.  A.  Etcheverry,  B.S.,  Irrigation  Expert. 
P.  T.  Bioletti,  B.S.,  Viticulturist. 

W.  T.  Clarke,  B.S.,  Assistant  Horticulturist  and  Superintendent  of  University  Exten- 
sion in  Agriculture. 

John  S.  Burd,  B.S.,  Chemist,  in  charge  of  Fertilizer  Control. 

J.  E.  Coit,  Ph.D.,  Assistant  Pomologist,  Plant  Disease  Laboratory,  Whittier. 

George  E.  Colby,  M.S.,  Chemist  (Fruits,  Waters,  and  Insecticides),  in  charge  of 
Chemical  Laboratory. 

H.  J.  Quayle,  M.S.,  Assistant  Entomologist,  Plant  Disease  Laboratory,  Whittier. 

H.  M.  Hall,  Ph.D.,  Assistant  Botanist. 

C.  M.  Haring,  D.V.M.,  Assistant  Veterinarian  and  Bacteriologist. 
E.  B.  Babcock,  B.S.,  Assistant  Agricultural  Education. 

W.  B.  Herms,  M.A.,  Assistant  Entomologist. 

J.  H.  Norton,  M.S.,  Assistant  Chemist,  in  charge  of  Citrus  Experiment  Station,  River- 
side. 
W.  T.  Horne,  B.S.,  Assistant  Plant  Pathologist. 
C.  B.  Lipman,  Ph.D.,  Soil  Chemist  and  Bacteriologist. 
R.  E.  Mansell,  Assistant  Horticulturist,  in  charge  of  Central  Station  grounds. 

A.  J.  Gaumnitz,  Assistant  Agronomist,  University  Farm,  Davis. 
N.  D.  Ingham,  B.S.,  Assistant  in  Sylviculture,  Santa  Monica. 

T.  F.  Hunt,  B.S.,  Assistant  Plant  Pathologist. 

P.  L.  McCreary,  B.S.,  Chemist  in  Fertilizer  Control. 

E.  H.  Hagemann,  Assistant  in  Dairying,  Davis. 

R.  M.  Roberts,  Farm  Manager,  University  Farm,  Davis. 

B.  S.  Brown,  B.S.A.,  Assistant  Horticulturist,  University  Farm,  Davis. 
J.  I.  Thompson,  B.S.,  Assistant  Animal  Industry,  Davis. 

Howard  Phillips,  B.S.,  Assistant  Animal  Industry,  Davis. 
J.  C.  Bridwell,  B.S.,  Assistant  Entomologist. 

C.  H.  McCharles,  M.S.,  Assistant  Agricultural  Chemical  Laboratory. 

E.  H.  Smith,  M.S.,  Assistant  Plant  Pathologist. 

C.  O.  Smith,  M.S.,  Assistant  Plant  Pathologist,  Plant  Disease  Laboratory,  Whittier. 

F.  E.  Johnson,  B.L.,  M.S.,  Assistant  Soil  Chemist. 

B.  A.  Madson,  B.S.A.,  Assistant  Experimental  Agronomist. 

Walter  E.  Packard,  M.S.,  Field  Assistant  Imperial  Valley  Investigation,  El  Centro. 

P.  L.  Hibbard,  B.S.,  Assistant  Fertilizer  Control  Laboratory. 

L.  M.  Davis,  B.S.,  Assistant  in  Dairy  Husbandry,  University  Farm,  Davis. 

S.  S.  Rogers,  B.S.,  Assistant  Plant  Pathologist,  Plant  Disease  Laboratory,  Whittier. 

L.  Bonnet,  Assistant  Viticulturist. 

H.  A.  Ruehe,  B.S.A.,  Assistant  in  Dairy  Husbandry,  University  Farm,  Davis. 

F.  C.  H.  Flossfeder,  Assistant  in  Viticulture,  University  Farm,  Davis. 

S.  D.  Wilkins,  Assistant  in  Poultry  Husbandry,  University  Farm,  Davis. 

C.  L.  Roadhouse,  D.V.M.,  Assistant  in  Veterinary  Science. 
F.  M.  Hayes,  D.V.M.,  Assistant  Veterinarian. 

F.  L.  Yeaw,  B.S.,  Assistant  Plant  Pathologist,  University  Farm,  Davis. 
M.  E.  Stover,  B.S.,  Assistant  in  Agricultural  Chemical  Laboratory. 

W.  H.  Volck,  Field  Assistant  in  Entomology,  Watsonville. 

E.  L.  Morris,  Field  Assistant  in  Entomology,  San  Jose. 

E.  E.  Thomas,  B.S.,  Assistant  Chemist,  Plant  Disease  Laboratory,  Whittier. 

A.  B.  Shaw,  B.S.,  Assistant  in  Entomology. 

G.  P.  Gray,  M.S.,  Chemist  in  Insecticides. 

H.   D.   Young,  B.S.,   Assistant  in  Agricultural   Chemistry,   Plant  Disease   Laboratory, 

Whittier. 
A.  R.  Tylor,  B.S.,  Assistant  in  Plant  Pathology,  Plant  Disease  Laboratory,  Whittier. 
E.  W.  Rust,  A.  B.,  Assistant  in  Entomology,  Plant  Disease  Laboratory,  Whittier. 
L.  T.  Sharp,  B.S.,  Assistant  in  Soils. 
W.  W.  Cruess,  B.S.,  Assistant  in  Zymology. 
J.  F.  Mitchell,  D.V.M.,  Assistant  in  Veterinary  Laboratory. 
J.  C.  Roper,  Patron,  University  Forestry  Station,  Chico. 
E.  C.  Miller,  Foreman,  Forestry  Station,  Chico. 

D.  L.  Bunnell,  Secretary  to  Director. 


CONTENTS. 


Page. 
HISTORICAL    151 

DISTRIBUTION 151 

ECONOMIC  IMPORTANCE 153 

Nature  of  Injury 154 

FOOD  PLANTS 155 

DESCRIPTION— LIFE  HISTORY— HABITS 157 

The  Egg    157 

Description    , 157 

Incubation  period    157 

Number    157 

Percentage  that  hatch 157 

Season  when  most  abundant 157 

Relation  of  weight  of  eggs  to  weight  of  body 158 

Hatching  records 159 

The  Active  Larva 160 

Description    160 

Emergence    160 

Locomotion    161 

Rate  of  travel  over  smooth  surfaces 163 

Rate  of  travel  over  sand  and  orchard  soil 163 

Other  factors  in  the  spread  of  the  young  scale 164 

Length  of  life  without  food 165 

Experiments  on  the  effect  of  temperature 165 

Effects  of  light 166 

Where  the  young  settle 167 

Proportion  of  young  becoming  fixed 168 

The  Fixed  Young 168 

Development  before  first  molt 168 

The  first  molt 169 

Development  between  first  and  second  molts 169 

The  second  molt  of  the  female 169 

Process  of  molting 169 

Effects  of  temperature . 169 

Honeydew  and  fungus  growth 170 

Relation  of  ants  to  the  scale 170 

Movement  after  settling 170 

The  Adult  Female 172 

Description 172 

Oviposition    172 

The  Development  of  the  Male 173 

The  second  stage  male 173 

The  male  puparium 173 

The  propupa 175 

The  pupa 175 

The  adult  male 175 

Seasonal   History   176 

Number  of  generations 176 

Mortality  at  different  seasons 177 

Annual  progeny  of  a  single  scale 178 


CONTENTS. 

Page. 
PARASITES   179 

SCUTELLISTA  CYANEA  Motscll 179 

History  of  introduction 179 

Economic  importance  and  present  status  in  California 180 

Distribution 181 

Description — Life  history- -Habits 181 

The  egg — Description — -Where  found — Length  of  stage 181 

The  Larva 182 

Description,  amount  of  food,  length  of  larval  life 182 

The  Pupa 183 

Description,  length  of  stage 183 

The  Adult 184 

Description    184 

Oviposition 184 

Proportion  of  the  sexes 185 

Pathenogenesis   185 

Length  of  adult  life 186 

Seasonal  History 186 

Number  of  Generations 186 

Hyperparasite.     Cerchysius  sp 187 

The  larva 187 

The  adult 187 

TOMOCERA  CALIFORNICA  How 189 

Description  and  life  history 189 

Aphycus  flavus  How 190 

The  larva,  pupa  and  adult 190 

Other  Internal  Parasites 191 

PREDACEOUS    ENEMIES 192 

Rhizobius    ventralis 192 

Orcus  chalybeus  and  other  Predators 193 

OTHER  SPECIES  OF  UNARMORED  SCALES  ASSOCIATED  WITH  THE 
BLACK    SCALE    194 

Saissetia  hemisphaerica 194 

Coccus    hesperidum 194 

Lecanium   corni    195 

Lecanium   pruinosum    196 

Lecanium    sp 196 

SYSTEMATIC    POSITION    198 

BIBLIOGRAPHY    199 


THE  BLACK  SCALE. 

SAISSETIA  OLEjE  Bern. 

By  H.  J.  Quayle. 

Assisted  by  E.  W.  Rust. 

HISTORICAL. 

The  Black  Scale,  Saissetia  olece  Bern,  is  widely  distributed  over  most 
of  the  countries  of  the  world,  and  has  been  known  as  a  pest  of  the  olive 
in  the  Old  World  nearly  as  far  back  as  our  entomological  records  go. 
It  was  first  described  by  a  Frenchman  named  Bernard*  from  specimens 
taken  on  olive  in  1782.  It  was  given  the  specific  name  olece  from  the 
host  plant  on  which  it  was  originally  found.  Articles  have  since 
appeared  on  this  insect  in  various  countries,  so  that  the  list  now  totals 
more  than  100  papers. 

Just  when  it  was  introduced  into  California,  or  from  what  country, 
doesn't  appear  to  be  established.  The  first  complete  account  of  its 
occurrence  here  is  given  in  Comstoc'k  's  report  for  ]  880.  It  had  been  in 
the  State,  however,  many  years  previous  to  that  time.  By  1880  it  was 
well  established  in  various  parts  of  the  State,  and  found  infesting  a 
wide  range  of  food  plants ;  but  it  was  at  that  time,  as  now,  a  particularly 
serious  enemy  to  citrus  trees.  It  was  given  the  common  name  of  "Black 
Scale  of  California. ' '  Since  this  was  the  first  reference  to  this  scale  in 
the  literature  of  this  country,  and  because  of  the  common  name  applied, 
it  appears  that  it  was  unknown  in  the  United  States,  at  that  time,  out- 
side of  California. 

DISTRIBUTION. 

The  following  localities  give  the  present  distribution  of  8.  olece  over 
the  world :  Aldabia,  Mauritius,  Europe,  New  Zealand,  Australia,  China, 
Japan,  Java,  Africa,  Ceylon,  Brazil,  W.  Indies,  Mexico,  France,  Italy, 
Spain,  Massachusetts,  South  Carolina,  Ohio,  Florida,  and  California. 

In  California  it  occurs  to  a  greater  or  less  extent  in  practically  all  of 
the  counties.  As  a  pest  it  is  limited  to  the  citrus  belt  of  southern  Cali- 
fornia, the  different  deciduous  trees  in  the  coast  counties  about  San 
Francisco  Bay,  and  to  some  extent  on  olive  trees  of  the  interior  valleys. 
It  occurs  throughout  the  valleys  on  oleander  and  olive  in  varying 
degrees,  but  is  not  often  serious  enough  to  warrant  treatment.  In  cer- 
tain places  in  the  lower  Sacramento  Valley  it  has  become  abundant 
enough  on  the  olive  to  necessitate  spraying. 

In  the  citrus  area  of  southern  California,  the  black  scale  is  the  most 

•1  Mem.  d'Hist.  Nat.  Acad.,  Marseilles,  p.  108    (1782). 


152 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


Bulletin  223] 


THE  BLACK   SCALE. 


153 


widely  distributed  of  all  the  scale  pests.  It  occurs  in  all  of  the  counties 
from  Santa  Barbara  to  San  Diego.  It  is  less  abundant  in  the  interior 
comities  of  Riverside  and  San  Bernardino;  but  even  here  in  some  sec- 


S  A  NTA 
BARBARA 


A 


,VENTURA\ 

^    ;\    LOS  ANGELES 

S*  4  ,J>° 


SAN 
BERNARDINO 


LosAnqeles^      -^jf" 


..  .ndheim\     ,  ,, 
/      ^         YJ^Corona 


Ge  /RIVERSIDE 


Fig.    2.— Distribution  of   Black   Scale  in   Southern   California. 

tions  it  becomes  an  important  pest.  But  the  black  scale  becomes  most 
abundant  nearer  the  coast  since  it  is  a  scale  that  is  more  adapted  to  the 
cooler  and  moister  climate  of  such  sections. 


ECONOMIC   IMPORTANCE. 

The  black  scale  is  probably  entitled  to  first  rank  as  a  citrus  fruit  pest 
in  southern  California.  It  has  this  place  in  Los  Angeles,  Orange,  and 
Santa  Barbara  counties.  This  is  based  upon  a  report*  of  the  respective 
horticultural  commissioners  of  those  counties.  In  two  other  counties, 
San  Diego  and  Ventura,  it  has  second  place  as  a  pest.  First  place  in 
San  Diego  County  is  preempted  by  the  purple,  but  because  of  the  wider 
distribution  of  the  black,  it  might  be  considered  as  the  more  important 
of  the  two.  In  Ventura  County  while  the  citrus  mealy  bug  is  put  first, 
the  commissioner  states  that  practically  all  the  control  work  is  directed 
against  the  black.  This  is  the  real  test  of  the  economic  importance  of 
an  insect,  so  that  the  black  scale  should  be  given  first  place  in  that 
county.  In  Riverside  and  San  Bernardino  counties  the  black  ranks 
third  as  a  pest.    In  these  counties  the  yellow  is  given  second  place,  but 


♦Bulletin  214,  Cal.  Ex.  Sta.,  p.  446,  1911. 


154 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


if  we  consider  the  red  (Chysomphalus  aurantii  Mask)  and  the  yellow 
(Chrysomphalus  aurantii  var.  citrinus  Coq.)  as  one  species  then  the 
black  will  occupy  second  place  in  these  two  counties.  It  will  be  noted 
also  that  the  Riverside  commissioner  stated  that  in  1910  seventy-five  per 
cent  of  the  control  work  was  directed  against  the  black.  This,  of  course, 
is  a  higher  percentage  than  is  usual  in  that  locality  for  the  black  scale. 
It  should  be  mentioned  also  that  where  the  purple  or  red  is  associated 
with  the  black,  the  control  work  is  usually  aimed  at  the  other  species, 
because  they  are  more  difficult  to  kill,  that  is,  providing  the  time  is 
chosen  when  the  black  is  in  the  right  stage.  But  if  the  black  were 
allowed  to  go  on  untreated  it  would  probably  do  as  much  as  or  more 
injury  than  the  others. 

Nature  of  Injury.  The  chief  injury  occasioned  by  the  black  scale  is 
not  due  so  much  to  the  loss  of  sap  through  feeding,  nor  to  the  toxic 
effect  on  the  tissues,  as  seems  to  be  the  case  with  the  armored  scales. 
That  more  or  less  injury  of  the  above  nature  is  done  is  not  questioned, 
for  it  must  be  this  largely  that  causes  an  actual  killing  of  twigs  where 

the  scales  are  incrusted 
upon  them.  But  so  far  as 
citrus  fruits  are  concerned, 
the  important  injury  is  due 
to  the  sooty  mold  fungus 
Meliola  camellice  (Catt) 
Sacc,  which  grows  in  the 
excretion,  or  so  called 
honey  dew.  Large  quanti- 
ties of  this  honeydew  are 
excreted,  which  falls  upon 
the  upper  surfaces  of  the 
leaves  and  fruit,  and  serves 
as  a  medium  for  the  growth 
of  the  fungus.  This  com- 
plete coating,  as  is  often 
found  on  the  leaf,  inter- 
feres with  the  natural  func- 
tions of  the  leaf  by  shutting  off  light.  Light  is  necessary  for  the  forma- 
tion of  starch  and  sugar,  and  consequently  the  sugar  content  of  the 
fruit  may  be  greatly  reduced.  The  interference  with  the  normal  func- 
tions of  the  leaves  also  tends  to  diminish  the  general  vigor  of  the  tree. 
But  the  great  injury  due  to  this  scale  is  simply  the  presence  of  the 
sooty  mold  fungus  on  the  fruit.  For  oranges  or  lemons  to  appear 
attractive  and  sell,  they  must  be  bright  and  clean.  The  proper  way  to 
get  such  fruit  is  to  keep  the  tree  free  from  the  causative  agent,  in  this 


Fig.  3. — The  sooty  mold  fungus.  Much  enlarged 
1.  Mycelium.  2.  Conidia.  3.  Pycnidia  with  im- 
mature spores.     From  Florida  Bulletin  No.  53. 


Bulletin  223]  THE  BLACK  SCALE.  155 

case  the  black  scale.  But  where  the  treatment  is  not  properly  done,  or 
not  done  at  all,  the  next  best  way  to  secure  clean  fruit  is  by  washing. 
This  operation  in  itself  adds  to  the  cost  of  handling,  but  the  most  im- 
portant injury  here  is  in  rendering  the  fruit  more  likely  to  decay.  With 
the  fruit  coming  in  contact  with  the  sides  of  the  tank,  brushes,  elevators, 
and  drying  racks,  it  is  impossible  to  escape  some  abrasions,  and  into 
these  abrasions  the  spores  of  the  following  fungi,  with  which  the  wash 
water  may  be  infected,  may  find  their  way:  Blue  Mold,  Penicillium 
italicum  Wehmer ;  green  mold,  Penicillium  digatum  Sacc. ;  brown  rot, 
Phythiacystis  citrophthora  Smith;  cottony  rot,  Sclerotinium;  Botrytis 
cinera  Pers.  and  Aspergillus  niger  Van  Tiegh. 


FOOD  PLANTS. 

While  the  total  list  of  food  plants  of  the  black  scale  is  a  long  one,  the 
number  that  is  seriously  infested  is  not.  large.  In  California  it  ranks 
first  as  a  pest  on  citrus  trees.  On  the  olive,  pepper  and  oleander,  it  also 
occurs  in  abundance,  and  often  does  much  injury,  but  it  is  only  rarely 
that  control  work  is  undertaken  on  these  trees.  Of  the  deciduous  trees 
the  apricot  and  prune  are  the  worst  attacked.  On  these  trees  Lecanium 
corni  is  often  associated  with  the  black,  and  is  the  more  important  pest 
of  the  two  in  the  deciduous  fruit  sections.  But  the  black  scale  often 
does  reach  the  status  of  a  pest  on  these  trees  and  spraying  is  done  to 
control  it.  It  is  not  uncommon  to  see  apricot  trees  completely  covered 
with  sooty  mold  fungus  as  a  result  of  black  scale  infestation. 

The  plants  named  practically  conclude  the  list  on  which  the  black 
scale  is  really  an  economic  pest  in  this  State.  Many  others  are  attacked, 
but  are  of  interest  chiefly  in  that  they  serve  to  reinfest  those  commercial 
trees  that  may  be  growing  about  them.  It  is  not  uncommon  to  find  a 
citrus  grove  with  the  borders  and  avenues  lined  with  peppers  or  olives. 
These  serve  as  an  excellent  breeding  ground,  for  they  remain  untreated. 
On  the  other  hand,  these  trees  are  believed  to  be  a  distinct  benefit 
because  they  insure  the  perpetuation  of  Scutellista,  in  the  interim  that 
the  scale  in  the  grove  itself  is  recovering  from  the  effects  of  fumigation. 
But  if  the  grove  is  regularly  fumigated,  and  the  Scutellista  thus  ignored, 
such  a  claim  is  illogical.  If  the  Scutellista,  by  being  maintained  on  the 
peppers,  tend  to  prolong  the  time  for  the  next  fumigation  then  they  are 
a  distinct  benefit.  Anyway,  such  shade  trees  as  the  pepper  seem  to  be 
necessary  for  the  comfort  and  aesthetic  value  they  afford,  and  since  it  is 
impossible  to  prevent  reinfestation  with  such  an  insect  as  the  black 
scale  anyway,  to  cut  down  such  trees,  as  is  sometimes  advocated,  hardly 
seems  justifiable. 


156 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


The  list  of  food  plants  from  which  the  black  scale  has  been  taken  is  as 
follows :  Orange,  lemon,  guava,  irish  juniper,  lombardy  poplar,  apricot, 
prune,  plum,  almond,  sycamore,  oleander,  pepper,  Rhus,  Heteromeles, 
Baccharis,  Ficus,  Habrothamnus,  Myosporum,  Melaleuca,  laurel,  holly, 


Fig.  4. — Black  Scale  (Saissetia  oleae  Bern.) 
on  orange  twig. 

beech,  ash,  Rhamnus,  Acer,  Grevillea,  Ligustrum,  night  shade,  Anti- 
desma,  Duranta,  Grewia,  Thespesia,  Cajanus,  apple,  pear,  olive,  pome- 
granate, Oregon  Ash,  honey  locust,  Magnolia,  Eucalyptus,  coffee,  rose, 
Vitis,  Camellia,  Terminalia. 


Bulletin  223]  THE  black  SCALE.  157 

DESCRIPTIONS— LIFE    HISTORY— HABITS. 

THE  EGG. 

Description.  The  eggs  are  oval  in  shape,  measuring  .3  mm.  long  and 
.2  mm.  wide.  When  first  deposited  they  are  usually  pearly  white,  but 
soon  change  to  a  cream  color  or  with  a  pinkish  cast.  As  the  develop- 
ment continues  they  pass  through  different  shades  of  pink  until  a  few 
days  before  hatching  they  assume  a  reddish  orange  hue.  The  eye  spots 
now  appear  and  the  embryo  may  be  made  out  within. 

Incubation  Period.  Several  hundred  freshly  deposited  eggs  were 
placed  in  a  pill  box  in  the  laboratory  on  June  9th.  On  June  24th  a 
few  hatched,  about  four  fifths  of  the  number  hatched  on  the  28th,  while 
the  last  hatched  on  the  29th.  The  minimum  incubation  period  under 
these  conditions  was  16  days  and  the  maximum  20  days.  Other  lots 
of  eggs  laid  on  June  16th  hatched  in  from  19  to  21  days.  During  the 
winter  season  hatching  may  be  prolonged  for  a  month  or  six  weeks. 

Number  of  Eggs.  Counts  made  of  the  number  of  eggs  from  10  differ- 
ent scales  of  various  sizes  were  as  follows:  319,  220,  2073,  839,  2058, 
2536,  1340,  1542,  2894,  2823.  The  number  will  thus  vary  from  about 
200  to  2900,  the  average  in  averaged  sized  scales  will  run  close  to  2000 
eggs. 

Percentage  of  Eggs  that  Hatch.  In  nearly  all  cases  practically  all  of 
the  eggs  hatch.  It  is  only  very  rarely  that  eggs  will  be  found  beneath 
the  scale  and  not  hatched.  But  it  is  rather  common  to  find  a  large  num- 
ber of  young  dead  beneath  the  parent.  This  is  probably  due  to  their 
inability  to  emerge  on  account  of  the  arch  at  the  posterior  tip  being  in 
close  contact  with  the  twig  or  through  the  clogging  of  the  opening  by  old 
egg  skins  or  young  that  have  died  from  some  other  cause.  It  is  possible 
also  that  extreme  heat  may  kill  the  young  before  they  emerge.  Heat  is 
an  important  factor  in  their  mortality  after  they  emerge. 

Season  when  Eggs  are  Most  Abundant.  The  eggs  of  the  black  scale 
may  be  found  in  certain  localities  at  any  season  of  the  year.  But  by 
far  the  largest  number  of  eggs  occur  in  the  spring  during  May,  June, 
and  a  portion  of  July.  At  this  season  the  great  majority  of  the  scales 
will  be  found  with  eggs  in  any  part  of  the  citrus  area,  but  at  other  times 
there  may  be  no  eggs  in  certain  groves,  while  in  others  eggs  will  be 
found.  In  this  connection  the  time  of  fumigation  may  have  an  impor- 
tant influence  on  the  stage  of  the  insect,  since  all  the  young  and  partly 
grown  may  be  killed,  while  the  eggs  under  the  adults  will  escape  the 
effects  of  the  gas.  But  there  is,  aside  from  this,  a  natural  off  hatch 
which  occurs  whether  the  tree  has  been  fumigated  or  not.  During  the 
season  of  1910  the  largest  number  of  eggs  were  present  in  the  latter 
part  of  May. 


158  UNIVERSITY  OF   CALIFORNIA — EXPERIMENT  STATION. 

Relation  of  Weight  of  Eggs  to  Weight  of  Body.  The  following  table 
gives  the  weight  of  the  scale  with  and  without  eggs,  the  difference  being 
the  weight  of  the  eggs  alone.  It  will  be  seen  that  the  eggs  comprise  a 
trifle  less  than  one  half  of  the  body  weight. 

1                              2                 3  4  5 

Weight  of  scale  and  eggs .014  grams  .018  .012  .019  .012 

Weight  of  scale .008  .008  .006  .009  .006 

Weight   of   eggs .006  .010  .006  .010  .006 

6  7  8  9  10 

Weight  of  scale  and  eggs .020  grams  .009  .017  .008  .007 

Weight    of    scale . .009  .005  .008  .005  .004 

Weight   of   eggs .011  .004  .009  .003  .003 

The  10  scales  indicated  in  the  above  table  were  picked  from  the  twigs 
with  their  full  quota  of  eggs  at  that  time.  This  was  when  the  eggs 
were  present  in  their  maximum  numbers.  All  of  the  eggs,  of  course, 
are  not  present  at  any  one  time,  since  the  period  of  oviposition  is  greater 
than  the  hatching  period.  Consequently,  more  eggs  would  be  deposited 
later  so  that  instead  of  the  weight  of  eggs  being  slightly  less  than  that 
of  the  body  as  indicated  in  the  table  the  total  number  laid  will  exceed 
one  half  the  body  weight. 

Hatching  Records.  The  scales  represented  in  the  following  table 
were  slightly  under  medium  size.  They  were  infesting  oleander  leaves 
and  each  one  was  surrounded  by  a  ring  of  tree  tanglefoot  so  that  the 
young  were  imprisoned  as  they  emerged.  Each  day  they  were  counted 
and  removed.  The  records  of  the  13th,  20th  and  27th  each  represent 
a  two  days'  hatch.  It  will  be  noted  that  the  hatch  roughly  follows  the 
temperature  changes.  During  the  cooler  weather  the  young  seem  to 
remain  under  the  scale  longer  and  emerge  in  larger  numbers  on  the  next 
warm  days. 


Bulletin  223] 


THE  BLACK   SCALE. 


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160  UNIVERSITY  OF   CALIFORNIA EXPERIMENT   STATION. 

THE  ACTIVE  LARVA. 

Description.  Length  .34  mm.,  width  .2  mm.  The  color  is  light 
brown ;  eyes  black,  antennas  6  segmented.  From  each  of  the  oval  plates 
there  arises  a  long  spine,  slightly  more  than  half  the  length  of  the  body. 
The  body  is  very  flat  and  oval  in  shape. 

Emergence.  In  all  cases  observed  the  yonng  larvae  make  their  way 
from  beneath  the  parent  under  the  arch  at  the  posterior  tip.  This  arch 
consists  of  a  slightly  raised  portion  of  the  scale,  for  a  short  distance  on 
either  side  of  the  anal  cleft,  which  is  not  attached  to  the  twig.  This  is 
large  enough  to  permit  of  the  exit  of  the  young  scales  and  occasionally 
two  have  been  seen  emerging  side  by  side.  The  emergence  occurs  at 
about  the  same  rate  as  the  hatch,  although  many  young  will  be  seen 
under  a  scale  at  one  time.  But  since  about  40  eggs  are  laid  in  a  day, 
this  number  may  hatch  at  the  same  time,  and  these,  together  with  the 
early  or  late  hatching  of  others  deposited  near  the  same  time,  accounts 
for  the  large  number  that  occur  under  the  scale.  They  may  remain 
under  the  scale  for  a  day  or  two,  so  that  when  they  emerge  they  have 
their  full  strength  and  begin  immediately  to  actively  crawl  about. 

Locomotion  of  the  Young  Larvce.  The  distance  traveled  by  the  active 
larva  on  smooth  paper  was  an  average  of  71  inches  during  a  two-hour 
period  when  the  temperature  was  73.5°  F.  The  higher  the  temperature 
the  faster  they  would  travel,  so  that  with  a  temperature  of  90°  F.  they 
traveled  in  the  same  time  a  distance  of  151  inches. 


Bulletin  223 J 


THE  BLACK   SCALE. 


161 


Fig.  5. — Tracings  of  young  black  scales  for  a  2-hour  period.     Reduced  7  times. 
Temperature  73.5  degrees.     Average  distance  71  inches. 


;'    ~'~~ — ~-.__ 

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Fig.  6. — Tracings  of  young  black  scales  for  a  2-hour  period.     Reduced  7  times. 
Temperature  80  degrees.     Average  distance  76  inches. 


162 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


Fig.  7. — Tracings  of  young  black  scales  for  a  2-hour  period.     Reduced  7  times. 
Temperature  83  degrees.     Average  distance  123  inches. 


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Fig.  8. — Tracings  of  young  black  scales  for  a  2 -hour  period.     Reduced  7  times. 
Temperature  90  degrees.     Average  distance  151  inches. 


Bulletin  223] 


THE  BLACK   SCALE. 


163 


Ex.  No. 


Table  Showing  Rate  of  Travel  Over  Smooth  Surface. 
Date. 


November  2,  1910. 
November  2,  1910_ 
November  2,   1910. 


July 
July 


1910. 
1910_ 


Time. 


Tempera- 
ture. 


1:45-  3:45 
1:45-  3:45 
1:45-  3:45 

2:15-  4:15 
2:15-  4:15 


3      i  August       17,   1910 9:30-11:30 

3         August       17,  1910 9:30-11:30 

3      I  August       17,   1910 9:30-11:30 


July 
July 
July 


1910_ 
1910_ 
1910. 


2:10-  4:15 
2:15-  4:15 
2:15-  4:15 


73.5° 

73.5° 
73.5° 

80° 
80° 

83- 
83° 

83° 

90° 

90° 
90° 

70  inches 
62  inches 
81  inches 

73  inches 
80  inches 


Average 
distance. 


71  inches 


76  inches 


103  inches  j 

140  inches 

127  inches  j    123  inches 

108  inches 

166  inches  j 

180  inches  I    151  inches 


EXPERIMENTS  ON  RATE  OF  TRAVEL  OVER  SAND  AND  ORCHARD  SOIL. 

May  31,  1910.  Temperature  84°  at  point  of  experiment.  3 :  30  p.  m. 
Several  dozen  young  (taken  from  under  adult)  were  placed  upon  leveled 
sand  in  a  dish.  At  3 :  55  one  reached  the  edge  of  the  dish,  at  4 :  02  two 
more,  and  5  more  at  4 :  30.  At  5  p.  m.  dozens  had  reached  the  edge  of 
the  plate.    The  distance  traveled  was  4  inches. 

June  1,  1910.  10 :  20  a.  m.  Temperature  78°  at  point  of  experi- 
ment. Several  active  young  were  liberated  in  the  center  of  a  plate  of 
average  lumpy  orchard  soil.  In  one  hour  10  reached  the  edge ;  at  noon 
about  50  more,  and  by  1  p.  m.  nearly  all  the  young  scale  had  reached 
the  edge  of  the  plate.     Distance  traveled,  4  inches. 

June  1,  1910.  9 :  15  a.  m.  Temperature  74°  to  84°.  Several  hun- 
dred young  were  placed  on  a  board  covered  with  fine  dust.  By  1  p.  m. 
nearly  all  had  died,  possibly  from  the  suffocating  effect  of  the  fine 
particles  of  dust.  The  most  active  had  traveled  but  28  inches.  Insects 
used  as  a  check  showed  no  ill  effects  under  the  same  conditions  except- 
ing that  they  were  on  clean  paper. 

June  1,  1910.  10 :  10  a.  m.  Temperature  80°  at  surface  of  sand. 
Several  hundred  young  were  liberated  in  the  center  of  a  dish  containing 
sand  with  the  surface  smoothed  over.  This  dish  was  then  placed  under 
a  cover  which  allowed  the  light  to  strike  strongly  on  one  side.  By 
10 :  50  a.  m.  the  majority  of  the  insects  had  reached  the  lighted  side  of 
the  box,  having  traveled  5  inches  in  40  minutes.  At  11 :  30  the  dish 
was  revolved  180°  and  the  insects  again  thrown  in  the  shadow.  By 
1  p.  m.  they  had  crossed  the  plate,  a  distance  of  10  inches  in  1J  hours. 
At  1 :  30  p.  m.  the  dish  was  again  revolved  and  the  insects  again  crossed 
the  10  inches  in  If  hours. 

June  3,  1910.  10:15  a.  m.  Temperature  85°.  A  plot  of  average 
orchard  soil  was  enclosed  within  strips  of  paper  each  2  feet  long.  In 
the  center  of  this  area  of  soil  400  or  500  active  young  were  liberated. 
By  12 :  30  p.  m.  about  20  insects  reached  the  edge;  by  1  p.  m.  nearly  50 
and  at  5  p.  m.  about  100.  Distance  traveled,  1  foot. 
2— bul.  223 


164  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 

June  3,  1910.  10:15  a.  m.  Temperature  85°.  A  plot  of  orchard 
soil  one  foot  square  was  enclosed  in  paper  and  in  the  center  of  this 
several  hundred  young  were  placed.  At  the  beginning  of  the  experi- 
ment the  morning  was  foggy.  At  11 :  05  three  insects  reached  the 
paper,  a  distance  of  six  inches.  By  this  time  the  sun  was  appearing 
and  the  temperature  rose  to  96°.  Later  102°  was  reached  and  all  the 
insects  died. 

June  9,  1910.  10:00  a.  m.  Temperature  73°.  A  plot  of  ordinary 
orchard  soil  two  feet  square  was  enclosed  with  strips  of  paper.  Several 
thousand  scales  just  removed  from  beneath  adults  were  liberated.  At 
11 :  30  four  reached  the  paper  and  at  noon  20  more.  Temperature  at 
this  time  was  76°. 

The  same  experiment  was  repeated  on  the  following  day  with  a  tem- 
perature of  72°  to  86°.  By  2  p.  m.  about  75  insects  reached  the  paper. 
The  same  was  repeated  on  the  following  day,  when  8  scales  reached  the 
paper  in  1  hour  and  5  minutes,  and  24  in  3  hours  and  50  minutes. 

July  18,  1910.  Temperature  80°,  humid.  Fifty  young  were  placed 
in  the  center  of  a  plot  of  sand  6  inches  in  diameter.  In  30  minutes  5 
reached  the  black  paper  on  which  the  sand  was  placed,  and  in  three 
quarters  of  an  hour  one  half  of  the  insects  had  reached  the  paper. 
Distance,  3  inches. 

From  the  above  experiments  it  will  be  seen  that  the  young  black  scale 
is  capable  of  traveling  some  distance  over  ordinary  orchard  soil,  but  the 
percentage  traveling  any  distance  is  very  small.  Much  greater  progress 
is  made  on  a  compacted  soil  than  over  a  fine  mulch.  It  may  be  pos- 
sible for  a  young  black  scale  to  make  its  way  from  one  tree  to  another, 
but  the  number  that  will  travel  that  distance  over  a  mulch  is  exceed- 
ingly small.  In  the  case  of  soil  compacted  after  a  heavy  rain  or  in  an 
irrigation  furrow,  it  is  possible  that  they  would  reach  even  the  second 
or  third  tree  away.  During  the  time  of  irrigation  they  may  also  be 
carried  by  the  flow  of  the  water  itself. 

Other  Factors  in  the  Spread  of  the  Young  Scale.  A  foot  bellows  was 
arranged  so  as  to  throw  a  current  of  air  against  a  white  screen.  The 
maximum  velocity  of  air  from  this  bellows  was  stronger  than  the  wind 
ever  blows  in  the  citrus  belt.  A  branch  containing  active  young  scales 
was  placed  in  this  current,  but  none  were  displaced  until  the  branch  was 
brought  to  within  six  inches  of  the  mouth  of  the  bellows.  Even  then 
many  withstood  the  extreme  velocity,  thus  showing  that  the  wind,  as  it 
ordinarily  blows,  can  not  be  counted  a  very  important  factor  in  dis- 
lodging the  young  black  scale.  Once  the  scales  were  dislodged,  they 
were  carried  a  short  distance  as  they  fell. 

Several  rags,  sticks,  pieces  of  boards,  and  a  pair  of  gloves  were  placed 


Bulletin  223]  THE  BLACK  SCALE.  165 

in  a  tree  badly  infested  with  the  young  black  scale.  Later,  when  these 
were  examined,  many  young  were  crawling  about  over  them.  It  is 
altogether  likely,  therefore,  that  ladders,  gloves,  clippers,  picking  boxes, 
and  other  things  used  in  the  harvesting  of  the  fruit  are  possible  means 
of  infesting  a  clean  grove  if  these  things  are  immediately  or  soon  used 
in  the  grove.  While,  then,  these  things  are  possible  sources  of  spread, 
they  are  not  so  important  as  natural  agencies. 

About  100  Coccinellids  were  confined  for  a  day  in  a  jar  containing 
olive  branches  badly  infested  with  black  scale  from  which  young  were 
issuing.  Upon  examination  it  was  found  that  young  scales  were  being 
carried  about  by  the  beetles.  About  one  beetle  in  every  10  or  15  carried 
from  one  to  four  scales.  The  slower  moving  beetles  were  most  likely  to 
carry  the  scales.  These  beetles  have  also  been  seen  under  the  natural 
conditions  of  the  field  to  have  young  scale  crawling  upon  them. 

What  has  thus  been  actually  observed  in  the  case  of  Coccinellids  is 
likely  to  occur  also  with  other  insects  that  frequent  scale-infested  areas. 
Among  these,  ants  may  be  mentioned,  but  these  are  not  likely  to  trans- 
port them  long  distances,  for  their  nests  are  usually  close  at  hand.  The 
larvae  of  Chrysopa  and  Hemerobius  which  may  feed  among  the  scales 
may  also  be  guilty  of  spreading  the  scales,  and  possibly  also  the  adults 
of  these  species.  Winged  Aphids  are  also  found  commonly  on  orange 
trees  in  the  early  spring,  principally,  but  these  are  more  apt  to  be  con- 
fined to  the  tender  growth  which  has  not  yet  become  infested  with 
scales.  But  of  all  the  active  insects  found  on  the  orange  tree  the 
Coccinellidce  are  probably  the  worst  offenders  in  spreading  young  scale. 

Length  of  Life  Without  Food.  Two  or  three  hundred  eggs  were 
taken  from  under  each  of  several  scales  and  as  the  young  hatched  they 
were  placed  in  pill  boxes  without  food.  One  lot  lived  about  52  hours ; 
another  60;  a  third  lot  (the  majority  about  60  hours),  while  a  few  lived 
for  65  hours ;  lot  4  lived  56  hours ;  lot  5  were  removed  from  under  the 
adults  alive;  these  lived  84  hours;  lot  6  were  similarly  taken  from 
beneath  the  parent  and  they  lived  84  hours.  Lots  7,  8,  9,  10  were  all 
taken  alive  from  under  the  adults  and  lived  66  hours  without  food.  It 
thus  appears  that  between  3  and  4  days  is  the  maximum  time  that  young 
black  scale  will  live  without  food. 

Experiments  on  the  Effects  of  Temperature  on  the  Young.  May  31, 
1910,  2  p.  m.  Temperature  115°  F.  in  sun  at  surface  of  ground.  Sev- 
eral hundred  active  young  (taken  from  under  adult)  were  liberated  on 
ordinary  orchard  soil.  At  2 :  15  when  again  examined  all  were  dead, 
not  having  moved  more  than  2  inches. 

June  30,  1910,  11  a.  m.  Temperature  80°  in  sun  4  feet  above  soil, 
Temperature  120°  with  bulb  in  soil  at  point  of  experiment.     Several 


166  UNIVERSITY  OF   CALIFORNIA — EXPERIMENT  STATION. 

hundred  young  liberated  on  ordinary  brown  colored  soil  died  within 
10  minutes. 

June  30,  1910,  11 :  05  a.  m.  Temperature  in  sun  6  feet  above  ground 
80°,  slight  wind.  Temperature  at  surface  of  paper  104°  to  110°, 
sheltered  from  breeze.  Active  young  removed  from  parent  w^re  lib- 
erated on  white  paper  under  above  conditions  and  remained  active  for 
2  hours,  after  which  observations  were  discontinued. 

June  30,  1910,  10 :  25  a.  m.  Temperature  94°  to  100°  at  surface  of 
cardboard.  Young  scales  were  placed  on  this  where  they  crawled  about 
for  2  hours  unharmed  by  the  heat. 

July  6,  1910.  Liberated  a  number  of  young  from  under  adult  on 
white  paper  in  the  sun.  Temperature  106°  to  110°.  Temperature  4 
feet  above  ground,  98°.  At  106°  they  were  very  lively,  but  as  the  tem- 
perature increased  they  moved  more  slowly  and  at  110°  almost  all  move- 
ment ceased,  although  a  2  hours'  exposure  did  not  kill  them. 

July  6,  1910,  11  a.  m.  Temperature  118°  at  surface  of  board  men- 
tioned below.  A  large  number  of  active  young,  taken  from  under 
female,  were  placed  upon  a  brown  colored  board.  Within  5  minutes  all 
the  scales  were  dead. 

July  7,  1910,  11  a.  m.  Temperature  130°  at  surface  of  soil.  Tem- 
perature 100°  four  feet  above  ground  in  sun.  Several  young  from 
under  female  were  placed  on  ordinary  orchard  soil  under  above  con- 
ditions. Death  resulted  within  5  minutes.  Insects  used  as  a  check  in 
the  shade  were  perfectly  normal. 

July  8,  1910,  10:30  a.  m.  Temperature  119°  to  122°  at  surface  of 
soil.  A  large  number  of  young  were  placed  upon  common  orchard  soil 
under  above  conditions.  After  15  minutes  they  were  again  examined 
and  found  dead,  a  check  lot  in  the  shade  remaining  normal. 

Effects  of  Light.  Several  experiments,  which  will  not  be  detailed 
here,  were  undertaken  to  determine  the  behavior  of  the  young  black 
scales  toward  light.  In  all  cases  they  responded  to  the  influence  of 
light,  showing  them  to  be  positively  phototropic. 

In  the  case  of  older  scales,  that  is,  when  they  migrate  from  leaves  to 
twigs,  since  they  almost  invariably  become  fixed  on  the  under  side,  it 
would  appear  that  they  later  in  life  become  negatively  phototropic. 

About  100  active  young  scales,  secured  from  beneath  a  female,  were 
placed  upon  the  middle  of  an  upright  stake.  Some  immediately  crawled 
downward,  but  a  large  majority  crawled  upward.  Upon  reaching  the 
top  these  did  not  remain  there,  but  crawled  down  again,  many  going 
directly  to  the  bottom.  A  little  later  they  became  distributed  all  over 
the  stake.  Here  the  effects  of  the  light  were  not  removed  so  that  it  can 
not  be  stated  whether  they  have  a  tendency  to  go  up  or  down..    But 


Bulletin  223]  THE  BLACK  SCALE.  167 

judging  from  observations  in  the  field  there  appears  to  be  a  tendency  to 
migrate  upward. 

Where  the  Young  Settle.  The  large  majority  of  the  young  in  most 
cases  select  the  leaves  as  a  place  to  settle.  They  may  choose  either  the 
upper  or  lower  surface.  If  the  leaves  are  exposed  to  the  sun  they  are 
more  apt  to  settle  on  the  lower  surface.  If,  too,  the  upper  surface  is 
covered  with  sooty  mold  fungus,  as  is  often  the  case,  they  are  more 
likely  to  select  the  cleaner  side  of  the  leaf. 

In  case  the  twigs  are  still  tender  a  considerable  number  of  young 
may  settle  there.  They  have  also  been  observed  to  settle  on  stems  that 
contained  more  or  less  of  the  corky  wood.  But  the  majority  upon  first 
settling  select  the  leaves  or  tender  stems.  To  be  sure,  the  old  scales 
are  found  on  very  large  limbs,  but  it  is  only  rarely  that  the  active  young 
settle  there.  The  old  are  found  there  usually  because  of  their  migration 
after  they  have  attained  some  size  on  the  more  tender  parts  of  the  tree. 

The  reason  for  thus  selecting  the  more  tender  parts  of  the  tree  is 
because  the  tissues  are  more  easily  penetrated  by  the  small  scales,  and 
because  the  liquid  parts  of  the  plant  are  nearer  the  surface  and  more 
easily  obtained.  There  is  a  tendency  of  many  scales  to  settle  along  the 
midrib  and  along  the  larger  veins.  They  fix  themselves  parallel  to 
the  midrib  with  the  central  line  of  the  body  at  the  bottom  of  the  ridge, 
one  half  extending  up  on  the  midrib  and  the  other  half  on  the  leaf 
surface.  This  may  be  partly  for  protection  since  there  is  a  distinct 
groove  here,  but  more  probably  because  the  sap  is  more  readily  obtained 
at  this  point. 

On  June  12,  1909,  160  active  young  were  liberated  on  twigs  and 
leaves,  80  on  the  twigs  and  80  on  the  leaves.  Upon  examination  on 
June  24th,  35  were  found  established,  and  these  all  on  the  leaves. 

On  the  same  date  150  scales  were  distributed  in  another  place  and 
on  the  24th  of  June,  57  were  found  on  the  leaves,  largely  along  the  mid- 
rib. On  July  30th  only  a  very  few  remained  alive,  and  an  occasional 
one  was  seen  on  the  branch. 

On  June  10,  1909,  12  young  black  scales  were  distributed  on  each  of 
the  leaves  of  a  terminal  twig,  excepting  the  lower  two.  Fourteen  days 
later  the  scales  which  had  settled  were  distributed  as  follows :  5  on  four 
leaves,  7  on  two,  13  on  one,  and  4  and  2  respectively  on  each  of  the  two 
lower  leaves  on  which  none  were  actually  liberated.  The  last  examina- 
tion, which  was  made  on  September  21st,  found  them  still  on  the  leaves. 

The  end  of  a  lemon  branch  was  isolated  with  tanglefoot  and  an 
infested  olive  branch  from  which  young  were  emerging  was  entangled 
in  the  twig.  Three  weeks  later  many  had  settled  on  the  leaves  and 
tender  branches,  most  on  the  upper  side,  fewer  on  the  lower  side  and 
least  on  the  tender  twigs.     Later  the  majority  of  those  dead  were  found 


168  UNIVERSITY  OF   CALIFORNIA — EXPERIMENT  STATION. 

on  the  upper  surface.  This  experiment  was  carried  on  in  several  dif- 
ferent places  in  the  Laboratory  plot  and  the  results  were  the  same  in 
each  case. 

The  following  table  gives  the  record  of  those  settling  in  our  breeding 
experiments  in  the  insectary.    Out  of  236  liberated  53  or  22.88  per  cent 


settled : 

No.  No. 

Date.                                                     Liberated.  Settled. 

May  17,1910 15  1 

May  17,1910 6  1 

June    6,1910 10  3 

May  10, 1910 4  2 

May  10,1910 6  3 

May     2,1910 11  5 

May     4,1910 7  4 

May     4,1910 5  1 

May     2,1910 7  4 


No.  No. 

Date.                                                     Liberated.  Settled. 

May   13,1910 6  0 

May     4,1910 6  1 

Aprill6,1910 7  2 

May     7,1910 15  2 

May     4,1910 5  2 

May  13, 1910 25  1 

May  13,1910 25  2 

May  17,1910 25  2 

May  17,1910 6  2 


May  11, 1910 6  2     j   May     2, 1910 20 

May  11,1910 6  3 

May  11,1910 6  3  Total    23G  53 

May  13,1910 7  0 

22.88  per  cent. 

Proportion  of  Young  Becoming  Fixed.  We  have  shown  that  in  the 
case  of  the  red  scale  about  41  per  cent  fails  to  become  settled.  The 
purple  is  a  little  more  successful  in  this  respect,  but  the  black  seems  to 
be  the  least  successful  of  the  three.  In  thousands  of  scales  liberated  we 
have  often  got  a  mortality  as  high  as  95  per  cent  before  they  became 
fixed.  In  other  cases  a  larger  per  cent  will  establish  themselves.  There 
appears,  therefore,  to  be  a  very  wide  variation  in  the  per  cent  that  may 
settle,  but  on  the  whole  it  is  very  small.  The  same  facts  have  been 
recorded  both  from  the  insectary  and  the  field.  Immense  numbers  of 
young  scales  have  been  found  settled  in  the  field  where  the  number  of 
adults  was  not  especially  large.  Again,  where  the  adults  are  extremely 
abundant  the  young  have  been  found  to  be  very  scarce.  This  statement 
is  made  too  with  due  regard  for  the  presence  or  absence  of  the  egg 
parasite,  Scutellista. 

THE  FIXED  YOUNG. 

Development  Before  First  Molt.  Soon  after  settling  the  young  scales 
become  flatter  and  somewhat  larger  in  area.  The  scale  preliminary  to 
the  first  molt  is  just  about  twice  the  size  of  the  young  after  hatching. 
The  length  at  this  stage  is  .7  mm.  and  the  width  .35  mm.,  as  compared 
with  .35  mm.  in  length  and  .2  mm.  in  width  before  settling.  The  anal 
plates  instead  of  being  at  the  extreme  tip  of  the  scale,  as  in  the  active 
larva,  are  now  drawn  considerably  forward,  or  rather  the  posterior  mar- 
gin of  the  body  has  extended  backward,  and  the  two  lobes  inward,  so 
that  the  plates  are  enclosed  in  a  triangular  space  some  distance  from  the 
tip.  The  long  spines  are  still  attached  to  the  anal  plates  but,  on 
account  of  the  plates  being  so  far  forward,  they  do  not  extend  as  far 
beyond  the  tip  of  the  body.     The  different  relative  position  of  the  anal 


Bulletin  223]  THE  BLACK  SCALE.  169 

plates  and  the  character  of  the  anal  cleft,  it  now  being  practically  closed 
behind  the  plates,  is  the  most  conspicuous  change,  aside  from  the  size, 
undergone  during  the  first  stage. 

The  First  Molt.  The  first  molt  occurs  from  a  month  to  six  weeks 
after  birth  during  the  summer  months,  and  this  may  be  prolonged  to 
two  months  or  more  during  the  winter  season.  There  is  considerable 
variation  in  the  time  of  molting,  even  though  the  scales  be  of  the  same 
age,  and  under  the  same  conditions.  We  have  found  this  same  fact  true 
for  the  cottony  cushion  scale,  there  being  as  much  as  two  months  differ- 
ence in  the  time  of  development  of  individuals,  hatched  on  the  same  day 
and  living  under  identical  conditions.  This  may  be  partly  due  to  pos- 
sible differences  in  food  supply,  as  well  as  to  individual  differences  in 
the  scales  themselves. 

Development  Between  the  First  and  Second  Molts.  The  change 
undergone  after  the  first  molt  is  not  very  striking  aside  from  the  begin- 
ning of  the  formation  of  the  letter  H.  At  this  time  the  ridge  that  forms 
the  bar  of  the  letter  extends  from  one  end  of  the  scale  to  the  other. 
Later  the  two  ends  become  obliterated  and  after  the  second  molt  the  true 
H  appears. 

The  Second  Molt  of  the  Female.  This  occurs  on  an  average  from 
about  two  and  a  half  to  three  months  from  birth,  during  the  spring  and 
summer  months.  In  winter  this  period  may  be  considerably  prolonged. 
While  there  is  more  or  less  variation  in  the  time  of  the  first  molt,  under 
the  same  conditions,  there  is  still  more  variation  with  the  second  molt. 
This  molt  brings  the  female  scale  to  the  adult  stage. 

Process  of  Molting.  The  process  of  molting  in  the  black  scale,  like 
other  unarmored  scales  studied  as  Coccus  hesperidum  and  Saissetia 
hemisphcerica,  consists  of  a  splitting  of  the  old  skin  at  the  anterior  end 
and  then  a  pushing  of  this  backward  until  it  is  free  from  the  insect. 

The  cast  skin,  which  is  a  very  minute  frail  object  rolled  up  more  or 
less,  may  sometimes  be  caught  still  adhering  to  the  posterior  tip  of  the 
body.  But  in  breeding  cages,  sealed  on  the  leaf  with  paraffin,  we  had 
no  trouble  in  detecting  these  after  they  were  completely  removed  from 
the  body.  Often  times  they  look  not  unlike  a  film  of  cotton,  and  the 
velvet  which  was  first  used  in  our  cages  to  prevent  the  insects  from 
escaping,  gave  us  much  trouble  in  distinguishing  the  molted  skins.  The 
antennas  beak,  legs  and  all  other  integumentary  structures  go  with  the 
molted  skin. 

Effect  of  Temperature.  The  effect  of  high  temperatures  has  already 
been  noted  in  the  case  of  the  active  larvae.  But  even  after  that  stage 
they  do  not  escape,  and  so,  after  the  scales  become  fixed  and  have  grown 
to  some  size,  hot  weather  periods  are  likely  to  kill  them  off  in  very  large 
numbers.    A  survey  of  the  black-scale-infested  territory  a  week  or  two 


170  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

after  one  of  these  hot  spells  will  show  that  in  some  cases  almost  the 
complete  generation  is  killed.  Scales  may,  of  course,  be  found  dead  in 
considerable  numbers  without  a  well-defined  hot  weather  period.  But 
the  killing  is  much  more  pronounced  and  uniform  after  such  a  period 
and  it  seems  logical  to  attribute  such  a  condition  to  it. 

Honeydew  and  Fungus  Growth.  The  excretion  from  the  black  scale, 
when  it  falls  upon  the  surface  of  the  tree,  offers  a  very  suitable  medium 
for  the  growth  of  the  sooty  mold,  Meliola  camellice  (Catt)  Sacc.  This 
fungus  is  associated  with  all  the  other  unarmored  scales  and  also  with 
the  insects  of  the  families  Aphididce  and  Aleyrodidce,  as  well  as  others 
of  less  importance  in  the  quantity  of  honeydew  excreted.  This  fungus 
is  a  saprophyte,  and  derives  its  sustenance  from  the  honeydew.  It  is 
not,  therefore,  directly  injurious  to  the  tree  as  a  parasitic  fungus  would 
be.  Indirectly,  however,  it  does  do  damage  to  the  tree  and  especially 
to  the  fruit,  as  previously  explained.  The  characteristic  black  covering 
formed  over  the  plant  is  due  to  the  vegetative  threads  of  the  fungus. 
It  is  spread  about  from  tree  to  tree  by  the  agency  of  the  wind  in  trans- 
porting the  spores. 

Relation  of  Ants  to  the  Scale.  It  very  commonly  occurs  that  trees 
infested  with  the  black,  as  well  as  other  unarmored  scales  and  particu- 
larly the  soft  brown,  will  have  ants  running  about  over  them.  The  ants 
are  there  for  the  purpose  of  getting  the  honey  as  it  is  excreted  by  the 
scales.  The  ants  by  a  stroking  with  their  antennas  induce  the  scales  to 
give  up  small  droplets  which  are  immediately  taken  into  their  bodies. 
The  ants  usually  do  no  harm  to  the  tree  directly,  unless  they  happen 
to  be  nesting  in  large  colonies  about  the  roots.  Occasionally  they 
do  attack  the  tender  growth,  eating  the  tissues  of  the  leaves  and  the 
tender  twigs.  But  indirectly  the  continual  movement  of  many  hun- 
dreds of  ants  over  the  scales  may  tend  to  prevent  oviposition  by  the 
parasites  of  the  scales.  This  is  especially  likely  to  be  true  in  the  case 
of  the  Argentine  species  which  infests  the  tree  in  such  immense  num- 
bers. On  the  other  hand,  cases  have  occurred  where  the  ants  were 
really  a  benefit.  The  chief  injury,  after  all,  in  the  case  of  the  black  scale 
is  in  the  honeydew  and  consequent  sooty  mold  rendering  unsightly  and 
unmarketable  the  fruit.  Ants  have  been  seen  numerous  enough  to  take 
up  all  the  honeydew  just  as  fast  as  it  was  excreted  and  completely  pre- 
vent any  sooty  mold  from  forming  on  the  plant  surface. 

Movement  After  Settling.  As  already  explained,  the  young  larvae 
settle  largely  upon  the  leaves.  This  is  true  also  in  the  case  of  deciduous 
trees.  It  is  also  true  of  such  other  unarmored  scales  as  have  a  similar 
life  history,  as  the  European  Fruit  Lecanium  {Lecanium  corni).  In 
the  case  of  such  scales  on  deciduous  trees,  they  must  migrate  from  the 
leaves  at  some  time  because  the  dropping  of  the  leaves  in  the  winter 


Bulletin  223] 


THE  BLACK   SCALE. 


171 


would  prevent  them  from  maturing.  And  so  they  do  transfer  them- 
selves to  the  twigs  as  the  leaves  complete  their  growth  in  the  fall  and 
become  yellow  and  dry.  Many  also  fall  to  the  ground  with  the  leaves, 
and  a  large  number  of  these  must  perish. 

The  same  vital  need  for  transferring  themselves  from  leaf  to  twig 
does  not  prevail  in  the  case  of  the  black  scale  on  citrus  trees.  But  it 
is  a  fact,  nevertheless,  that  only  a  very  few  adult  black  scales  are  ever 
found  on  the  leaves.  There  is,  therefore,  a  transfer  from  leaf  to  twig, 
since  the  majority  of  the  young  settle  on  the  former.  This  occurs  when 
the  scale  is  partly  grown.  The  exact  time  varies  greatly  and  is  probably 
dependent  upon  the  food  supply.     In  the  case  of  the  young  first  settling 


Fig. 


-Mature  Black  Scales. 


it  has  been  stated  that  the  leaves  are  chosen  because  of  the  tissues  there 
being  more  easily  penetrated  and  the  liquid  food  nearer  to  the  surface, 
and  thus  more  likely  to  be  available  through  the  short  beak  of  the  young. 
On  the  other  hand,  as  the  scales  become  older  and  the  beak  larger  and 
stronger,  they  are  more  likely  to  get  a  greater  supply  of  food  from  the 
twigs,  through  whose  tissues  they  are  at  this  time  able  to  penetrate. 
But  it  may  be  an  instinctive  provision,  too,  to  choose  the  more  perma- 
nent part  of  the  tree  for  their  final  resting  place.  While  a  leaf  on  a 
citrus  tree  may  remain  for  two  or  three  years,  on  the  other  hand  it  is 
liable  to  drop  off  as  in  the  case  of  a  deciduous  tree. 

A  drying  of  a  leaf  or  some  other  abnormal  condition  will  cause  the 
scales  to  loosen  their  hold  and  move  about  while  they  are  still  very 
young,  that  is,  before  the  first  or  second  molt.  But  ordinarily  the 
greatest  migration  occurs  later  and  after  the  second  molt.  This  period 
from  settling,  will  thus  be  after  three  months  and  later.  Scales  have 
been  observed  moving  about  when  they  had  attained  a  length  of  2 J  mm. 
The  smallest  mature  scales  do  not  exceed  this  length,  though  they  are,  of 


172  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 

course,  greater  in  height.  Usually  in  the  migrating  stage  they  are  still 
elongate  and  not  so  broad  as  they  become  later.  But  many  in  the 
so-called  rubber  stage  have  that  broadened  effect,  and  will  be  seen  mov- 
ing about  looking  for  a  suitable  place  to  become  permanently  fixed. 

THE  ADULT  FEMALE. 

After  the  second  molt,  which  brings  the  female  to  the  adult  stage, 
there  is  a  very  great  increase  in  size,  and  also  in  general  form.  The 
more  or  less  elongate  scale  lying  flat  on  the  surface  is  now  almost  round, 
and  has  become  greatly  thickened.  The  letter  H  is  very  distinctly  out- 
lined on  the  dorsal  surface.  As  it  approaches  the  egg-laying  stage 
many  specimens  become  a  dark  mottled  gray.  When  egg-laying  is 
begun,  the  scale  takes  on  a  more  leathery,  smoother  surface  and  also 
becomes  much  darker  in  color,  this  varying  from  a  dark  brown  to  a  jet 
black. 

The  size  of  the  adult  varies  from  a  height  of  1  to  3  mm. ;  length,  2\ 
to  5£  mm. ;  width,  2  to  4f  mm.  This  represents  about  the  extremes  in 
size,  and  individuals  will  be  found  at  all  sizes  between  these  dimensions. 
Usually  on  the  same  tree  the  majority  of  the  scales  will  be  of  about  the 
same  size.  Nearly  always  on  young,  healthy  trees  the  scales  will  be 
vigorous  and  of  good  size.  In  other  cases,  and  frequently  on  olive  trees, 
all  the  scales  will  be  small.  The  condition  of  the  tree,  and  the  number 
of  individuals,  appear  to  be  the  most  important  factors  in  determining 
the  size.  Where  the  scales  are  simply  crowded  against  one  another,  and 
deformed  for  lack  of  room  for  normal  growth,  they  are  usually  of  small 
size. 

Oviposition.  Usually  from  eight  to  ten  months  are  necessary  to  bring 
the  female  to  the  egg-laying  stage.  The  number  deposited  varies  from 
200  to  about  3,000,  with  an  average  of  1,500  or  2,000.  The  oviposition 
period  lasts  from  six  weeks  to  two  months  or  longer. 

On  May  7,  1910,  several  solitary  scales  were  selected  on  oleander 
leaves  and  each  enclosed  with  rings  of  tanglefoot.  Young  were  issuing 
from  under  them  at  the  time,  so  that  they  must  have  begun  egg-laying  at 
least  20  days  previously.  On  the  31st  of  July  young  were  still  issuing 
from  under  the  adults.  When  these  were  overturned  there  were  still 
enough  eggs  to  hatch  for  a  week  longer.  The  known  egg-laying  period 
is  thus  55  days,  and  the  evidence  points  to  at  least  10  days  longer.  On 
the  10th  of  August  the  last  eggs  hatched  from  one  of  these  scales,  mak- 
ing a  known  length  of  64  days,  with  possibly  a  week  added  on  to  this  at 
the  beginning.  A  good  healthy  black  scale  will,  therefore,  deposit  an 
average  of  30  or  40  eggs  a  day  for  a  period  of  60  days.  If  an  egg- 
laying  female  is  removed  from  its  natural  resting  place,  it  will  continue 
to  deposit  eggs  for  several  days.     The  following  table  gives  the  results 


Bulletin  223]  the  black  scale.  173 

of  isolating  egg-laying  individuals  in  pill  boxes  to  determine  the  extent 
of  oviposition  when  removed  from  their  food  plant.  The  scales  were 
taken  from  the  twigs  and  all  eggs  removed  on  May  3d : 

Oviposition   When  Removed  from  Food  Plant. 
Scale 
No.  May  4.       May  5.        May  6.         May  7.       May  8.       May  9.      May  10.      May  11.      May  18. 

1   30  72         122        152         ___         303        315 

3  ~~~IIII-I     62         106         183        254         "I         397        427         I"         HZ 

4   64         148         218         300         340 

5   50  98         138         195         275         ___         480         510        648 

6   163         244         362         510         627         ___         800         824 

THE  DEVELOPMENT  OP  THE  MALE. 

While  the  black  scale  is  very  widely  distributed  over  the  world,  little 
has  been  known  and  practically  nothing  published  about  the  male.  It 
was  first  described  by  Dr.  B.  W.  Griffith*  of  Los  Angeles  in  1893.  It 
was  thus  said  to  be  limited  to  a  small  area  in  the  vicinity  of  Los  Angeles. 
During  the  past  year  or  two  we  have  taken  it  at  various  places  in  the 
citrus  belt  from  Santa  Barbara  to  San  Diego.  It  seemed  to  be  especially 
abundant  during  the  season  of  1909.  In  places  where  it  occurred  that 
year,  it  was  not  nearly  so  abundant  on  the  previous  year  or  the  year  fol- 
lowing. As  many  as  97  puparia,  from  all  of  which  males  had  emerged, 
have  been  seen  on  a  single  orange  leaf.  The  males  have  been  taken  from 
the  leaves  of  orange,  oleander,  pepper  and  olive.  They  emerged  during 
the  months  of  June,  July,  August,  September,  October,  November, 
December,  and  possibly  other  months,  though  not  actually  observed. 

The  Second  Stage  Male.  Up  to  the  time  of  the  first  molt  there  is  no 
difference  between  the  sexes.  After  the  first  molt  the  male  becomes 
decidedly  more  elongate,  resembling  more  nearly  a  partly  grown  soft 
brown  scale.  Its  length  is  1.5  mm.  and  width  .64.  It  is  of  a  light  brown 
color  with  the  eyes  visible  in  the  latter  part  of  the  stage  as  small  dark 
areas  on  the  front  margin.  The  anal  plates  together  form  a  triangle 
with  rounded  corners,  and  from  the  tip  of  each  of  these  there  arises 
3  or  4  small  spines,  and  one  large  one  on  the  central  dorsal  surface. 

The  length  of  time  spent  in  this  stage  is  about  four  weeks.  During 
this  time  it  is  feeding  and  grows  to  about  5  times  the  length  of  the  just- 
hatched  larva.  At  the  end  of  the  stage  a  puparium  is  formed  which 
completely  covers  the  insect  although  it  is  transparent  and  not  so 
readily  discernible. 

The  Male  Puparium.  This  puparium  is  a  glassy-like  covering  that 
is  formed  from  the  secretion  of  numerous  pores  over  the  body  surface. 
Its  length  is  1J  mm.  and  width  .5  mm.  The  surface  is  slightly  roughened 
with  a  row  of  granular  projections  along  the  dorsal  line.  Two  lines 
beginning  at  the  anterior  end  converge  upward  for  a  short  distance  and 
then  run  more  nearly  parallel,  with  but  a  slight  convergence  toward  the 

*Ent.  News,  vol.  XXII,  no.  4,  p.  167,  1911. 


174 


UNIVERSITY  OF   CALIFORNIA — EXPERIMENT   STATION. 


posterior  end.  Within  this  the  surface  is  more  convex,  forming  a  ridge 
along  the  dorsal  line.  Not  quite  one  quarter  of  the  distance  from  the 
anterior  end  and  at  a  point  where  the  lines  begin  to  run  parallel,  is  a 
cross  line  or  carina.  Another  lateral  carina  crosses  this  dorsal  strip,  or 
coronet,  at  one  quarter  the  distance  from  the  posterior  end.  Imme- 
diately posterior  to  this  cross  line  are  two  spiracular  channels  extending 
to  either  margin.  The  other  two  spiracular  channels,  extending  from  the 
coronet  to  either  side,  are  just  before  the  middle  line.  There  is  a 
triangular  opening  for  the  anal  plates  and  a  cleft  from  this  to  the 
posterior  end.  Along  the  margin  is  a  series  of  circular  pores  from  which 
secretions  extend  to  the  surface  of  the  leaf,  thus  holding  the  puparium 
in  place.    When  a  puparium  was  removed  3  or  4  weeks  after  the  male 


>*^k 


w 


Fig.   10. — Development  of  the  male  of  the  Black  Scale. 
1.   Second  stage.     2.  Propupa.     3.     Pupa.     x40. 

had  emerged,  these  connecting  threads  were  still  capable  of  being 
stretched  considerably  as  was  observed  upon  lifting  the  puparium. 

These  are  found  usually  on  the  under  side  of  the  leaves  of  the  orange, 
pepper,  olive  and  oleander,  chiefly,  since  these  constitute  the  principal 
food  plants  of  the  scale.  When  the  insect  is  still  beneath  it  can  be 
detected  through  this  transparent  covering.  If  it  has  not  yet  trans- 
formed to  the  propupa  it  occupies  the  entire  space  beneath  extending 
well  out  to  the  margins,  but  in  the  case  of  the  later  stages  the  insect 
beneath  is  somewhat  narrower.  These  puparia  may  remain  on  the  leaves 
for  months  after  the  scale  has  emerged. 

The  second  stage  male  is  capable  of  moving  up  to  the  time  the 
puparium  is  secreted,  which  is  the  preliminary  step  in  the  change  to 
the  propupa.     But  it  is  only  rarely  that  any  movement  occurs  in  this 


Bulletin  223] 


THE  BLACK   SCALE. 


175 


stage,  and  hence  the  males  are  nearly  always  found  on  the  leaves  where 
the  young  first  settle. 

The  Propupa.  Length  1.4  mm.,  greatest  width  .4  mm.  Color  light 
brown  with  red  pigment  scattered  about,  particularly  at  posterior  end; 
head  reddish ;  eyes  dark  red  or  brown.  Sheath  of  style  short  and  blunt ; 
on  either  side  of  the  style  are  two  more  slender  and  pointed  appendages, 
the  cerci  extending  beyond  the  style.  At  the  tip  are  a  few  short  hairs  or 
spines.  The  sheaths  of  the  antennae  and  legs  are  scarcely  visible  on  the 
dorsal  surface  excepting  a  broadening,  where  these  lie  on  the  ventral 
margin.  On  the  ventral  side  these  are  plainly  visible,  and  lie  in  close 
contact  with  the  body.  The  length  of  the  propupal  period  is  from  5  to  8 
days  during  the  warmer  weather. 

The  Pupa.  Length  1.2  mm.,  width  .4  mm.,  general  color  same  as  that 
of  propupa,  excepting  that  there  is  a  larger  amount  of  pigment  at  the 
anterior  end.  The  head  is  entirely  red.  A  marked  constriction  forms 
the  neck  making  the  head  appear  as  arrow-shaped.  Eyes  black.  The 
wing  pads  are  conspicuous  and  extend  to  third  abdominal  segment.  The 
style  has  increased  in  length  so  that  it  is  slightly  longer  than  the  cerci 
on  either  side.  The  antennas,  legs  and  wing  pads,  while  naturally  lying 
close  to  the  body,  are  distinct  and  readily  separated  from  it. 

Eight  to  twelve  days  are  spent  in  the  true  pupal  stage,  when  it 
changes  to  the  adult.  In  all  the  molts  after  the  second  stage  the  skin  is 
split  at  the  anterior  end  and  pushed  back  beyond  the  puparium. 

The  Adult  Male.  The  fully  developed  male  remains  from  1  to  3  days 
beneath  the  puparium  before  emerging.  The  adult  stage  can  be  deter- 
mined without  the  removal  of  the  pu- 
parium  by  the  appearance  of  the  long 
white  caudal  filaments  which  project 
out  beyond  the  tip  of  the  puparium. 
The  life  of  the  adult  male  is  from  one 
to  four  days.  The  following  descrip- 
tion of  the  male  is  copied  from  the 
notes  of  Prof.  R.  W.  Doane,  who 
worked  with  the  writer  during  the 
summer  of  1910: 

Length  exclusive  of  style  1  mm. ; 
style  .4  mm. ;  caudal  filament  8  mm. ; 
antennae  5  mm. ;  wing  1  mm.  long, 
.5  mm.  wide;  honey  yellow;  head 
darker  yellow ;  anterior  pair  of  upper 
eyes  dark  red,  posterior  pair  black,  smaller;  ventral  pair  black  equal 
in  size  to  the  upper  anterior  pair.  Antennae  whitish,  10  jointed,  first 
joint  short,  thick  cylindrical;  second  joint  about  equal  to  first,  but 


Fig.  11.— Male  of  Black  Scale.     x25. 


176  UNIVERSITY  OP   CALIFORNIA — EXPERIMENT  STATION. 

oval;  third  joint  about  as  long  as  second,  but  much  more  slender, 
slightly  swollen  toward  the  tip;  remaining  joints  all  slender,  cylin- 
drical, fourth  as  long  as  fifth  and  sixth  together;  others  subequal  in 
length,  collar  long,  cylindrical;  prothorax  broad  shield  shaped;  meso- 
thorax  more  strongly  chitinized  and  wholly  brown  except  a  yellow 
shield-shaped  area  above,  between  the  bases  of  the  wings;  metathorax 
with  a  slight  brownish  tinge;  legs  brownish  yellow;  style  yellow; 
caudal  filaments  white,  slender,  tapering,  twice  as  long  as  style;  wings 
hyaline  with  a  yellowish  tinge,  with  a  microscopic  close-set  pubescence. 

The  above  description  is  given  in  detail  because  the  original  descrip- 
tion given  by  Dr.  Griffith  is  incomplete.  The  only  figures  of  the  male 
that  have  appeared  from  original  specimens  are  given  by  Marlatt  in 
the  United  States  Department  of  Agriculture  year-book  for  1900.  "In 
the  figure  of  the  adult  there  given  the  black  bands  are  not  properly 
placed.  Both  are  too  far  forward,  the  first  is  not  broad  enough,  the 
second  too  broad,  and  the  yellowish  spot  between  the  wings  does  not 
reach  to  the  base  of  the  wings. ' ' — Doane. 

When  the  males  emerge  the  females  that  hatched  at  the  same  time 
have  completed  their  second  molt,  and  the  letter  H  is  evident.  Sum- 
marizing the  length  of  the  life  cycle  of  the  male  it  will  be  during  the 
summer  months  as  follows:  1st  stage,  1-|  months;  2d  stage,  1  month; 
propupa,  8  days ;  pupa,  10  days ;  adult,  3  days ;  total,  96  days,  or  about 
3  months. 

SEASONAL  HISTORY. 

Number  of  Generations.  There  is  usually  but  one  complete  genera- 
tion of  the  black  scale  in  a  season.  The  great  majority  of  these  come 
to  maturity  in  the  spring  months,  so  that  most  of  the  eggs  are  deposited 
by  midsummer.  The  time  of  maturing  of  the  bulk  of  the  black  scales 
will  vary  somewhat  from  year  to  year,  and  in  some  years  there  will  be  a 
much  more  uniform  hatch  than  others.  Taking  a  specific  season,  as 
1910  in  the  Los  Angeles  district,  the  height  of  egg-laying  was  during 
the  third  week  in  May.  The  greatest  production  of  young  was  about 
the  third  week  in  June.  Eggs  will  be  deposited  by  a  single  scale  during 
a  period  of  two  months.  By  the  middle  of  July,  therefore,  most  of  the 
young  had  already  appeared. 

On  June  3,  1910,  sixteen  different  lots  of  young  black  scale  were 
distributed  in  twig  cages  on  different  orange  trees.  These  remained 
small  throughout  the  summer,  fall  and  winter,  beginning  to  grow  rapidly 
in  February  and  March,  so  that,  when  examined  on  April  26,  1911,  some 
had  not  yet  begun  egg  laying,  others  had  just  started,  while  others  had 
been  depositing  eggs  for  a  week  or  two.  By  the  middle  of  May  or  first 
of  June,  young  were  emerging  from  most  of  these  scales.  Practically 
one  full  year  was  thus  necessary  to  bring  these  scales  from  the  period 


Bulletin  223]  THE  BLACK  SCALE.  177 

of  active  young  to  the  time  when  active  young  were  in  turn  emerging 
as  progeny  of  these  scales. 

On  March  15,  1911,  a  large  number  of  active  young  were  liberated 
on  a  small  potted  orange  tree  that  had  first  been  fumigated  and  very 
carefully  inspected  so  that  it  was  absolutely  free  from  any  scale.  On 
August  4,  1911,  eggs  were  found  under  some  of  these  scales  which  had 
been  liberated  4-J  months  before.  The  scales  were  very  small  and  were 
probably  stimulated  to  unusually  early  oviposition  on  account  of  the 
scarcity  of  food,  as  the  tree  by  this  time  was  nearly  dead.  On  August 
10,  young  had  commenced  to  hatch  and  settle  making  the  period  from 
young  to  young  approximately  five  months.  This  experiment  verifies 
what  has  been  observed  in  the  field,  namely,  that  in  the  case  of  young 
scales  appearing  very  early  in  the  spring  they  are  very  likely  to  com- 
plete their  development  before  the  following  winter. 

On  May  22,  1911,  young  black  scales  were  liberated  on  small  potted 
pepper  trees  out  of  doors.  When  examined  on  September  8,  1911,  8  or 
10  scales  were  found  with  eggs  beneath.  Counting  the  usual  hatching 
period  the  life  cycle  in  this  case  would  be  completed  in  just  four  months. 

The  young  hatching  from  the  large  spring  brood  in  June  and  July 
settle  on  the  leaves  largely,  where  they  grow  very  slowly.  Between  a 
month  and  two  months  the  first  molt  occurs,  and  after  an  interval  of 
about  the  same  length  the  second  molt  of  the  female  occurs.  This  brings 
it  well  into  the  fall,  and  from  that  time  on  migration  occurs  from  the 
leaves  to  their  permanent  abode  on  the  twigs  and  branches.  The  winter 
is  passed  as  a  partly  grown  insect.  It  has  molted  twice  and  is  mature, 
but  is  still  of  comparatively  small  size.  With  the  first  period  of  growth 
of  the  citrus  tree  in  the  spring,  and  the  rise  in  temperature,  they  grow 
rapidly  to  full  size,  and  are  depositing  eggs  by  the  first  of  May.  Those 
scales,  which  hatch  very  early  in  the  spring  and  have  all  of  the  warmer 
period  of  the  season  to  hasten  their  development,  will  mature  in  the  fall 
and  thus  complete  their  life  cycle  in  a  shorter  time.  The  old  scales  die 
very  soon  after  their  quota  of  eggs  is  deposited. 

While  the  above  history  applies  to  the  great  number  of  scales  generally 
over  the  citrus  belt,  there  is  much  variation  in  certain  places  as  applies 
to  the  bulk  of  the  scales  as  well  as  to  individuals  scattered  about  every- 
where, that  are  out  of  season  with  the  majority.  Their  long  period  of 
development,  through  which  outside  factors  have  an  opportunity  to 
exert  their  influence,  and  the  congenital  differences  within  themselves, 
as  well  as  the  artificial  interference  through  fumigation  must  largely 
account  for  this  variation. 

Mortality  at  Different  Seasons.  The  season  of  greatest  mortality  of 
the  black  scale  is  during  the  summer  months,  and  particularly  during 
the  hot  weather  periods.  But  the  season  alone  is  not  responsible,  for 
the  stage  of  the  insect  is  equally  as  important.    It  is  during  the  younger 


178  UNIVERSITY  OF   CALIFORNIA — EXPERIMENT  STATION. 

stages  that  the  great  mortality  occurs,  and  this,  likewise,  is  in  the 
summer  season.  In  another  place  it  has  been  shown  that  less  than  23 
per  cent  succeed  in  getting  established  after  hatching.  Many  in  our 
breeding  cages  died  before  they  reached  the  first  molt  and  the  molting 
period  itself  was  a  critical  period  when  many  more  died.  During  the 
time  of  development,  therefore,  or  until  they  have  transferred  them- 
selves to  the  twigs,  there  is  much  loss  by  death  from  one  cause  or 
another.  After  they  become  fixed  on  the  twigs  there  is  comparatively 
little  loss  of  life.  Such  parasites  as  Aphycus  flavus  will  attack  them, 
and  there  may  be  some  loss  by  Coccinellids,  but  even  these  prefer  the 
scales  in  their  younger  stages.  Even  Scutellista,  which  attacks  the 
scale  when  it  is  mature,  has  no  effect  on  the  adult  scale,  for  it  confines 
itself  very  largely  to  feeding  on  the  eggs. 

Annual  Progeny  of  a  Single  Scale.  While  the  total  number  of  eggs 
from  a  single  scale  may  approach  3,000  in  number,  it  is  but  an  exceed- 
ingly small  per  cent  that  ever  reaches  maturity.  A  tree  having  black 
scale  may  become  very  badly  infested  in  a  single  year.  This  is  especially 
true  of  well  cared  for  citrus  trees.  It  is  also  a  common  observation  that 
fumigated  trees  become  reinfested  more  rapidly  than  one  that  has  not 
been  fumigated.  In  many  places  trees  infested  with  scale  have  never  been 
fumigated,  and  the  number  of  insects  present  seems  to  remain  almost 
stationary.  In  such  cases  the  number  of  the  progeny  only  replaces  the 
number  of  the  adults  whose  places  they  have  taken.  This  is  true  gen- 
erally of  an  insect  after  it  has  become  established.  In  the  case  of  a  new 
introduction,  as,  for  example,  the  San  Jose  scale,  Colorado  potato  beetle, 
cabbage  butterfly,  and  a  host  of  others,  the  progeny  that  matured  at 
first  was  prodigious.  But  these  insects  after  a  few  years,  when  they 
become  well  established,  have  since  maintained  themselves  in  about  the 
same  numbers,  or,  if  anything,  there  has  been  a  slight  decrease. 

So  with  the  black  scale  where  artificial  control  is  not  practiced  the 
actual  progeny  reaching  maturity  only  replaces  the  parents.  In  case 
of  insects  where  the  male  is  so  rare  as  that  of  the  black  scale,  this  means 
that  only  one,  or  at  most  two,  of  the  total  number  of  young  produced 
reach  maturity.  Of  course,  there  may  be  yearly  fluctuations,  but  for  a 
term  of  years  it  will  hold  true.  An  effort  was  made  to  determine  the 
actual  progeny  of  the  black  scale  under  normal  conditions.  Ten  small 
olive  trees  were  selected  and  on  each  of  six  there  was  a  single  black 
scale,  and  on  the  remaining  four  there  were  two  present  on  each.  These 
were  examined  4J  and  6  months  later  with  the  following  result:  On 
tree  No.  1  was  one  scale ;  on  No.  2  no  scale  aside  from  the  original  one ; 
on  No.  3  one;  No.  4  and  5  two  each;  No.  6  no  new  scales;  No.  7  three 
scales;  No.  8  two;  No.  9  none;  No.  10  one.  If  this  experiment  were 
repeated  a  number  of  times  there  would  probably  be  as  many  variations 


Bulletin   223]  THE    BLACK    SCALE  179 

as  experiments,  but  the  total  together  would  result  very  much  the  same 
as  this  single  one,  namely,  that  the  progeny  maturing  would  be  approxi- 
mately equal  to  the  number  of  parents  that  gave  them  birth. 


PARASITES. 

Scutellista  cyanea  Motsch. 
The  most  important  insect  enemy  of  the  black  scale  in  this  State  is 
Scutellista  cyanea  Motsch.  It  was  introduced  into  the  State  in  1900  and 
has  since  become  well  distributed  in  most  of  the  sections  where  the  scale 
occurs  in  injurious  numbers.  The  percentage  of  scales  parasitized  often 
runs  as  high  as  75  per  cent,  but  this  varies  greatly  in  different  sections 
and  in  the  same  section  in  different  years.  In  1910  Scutellista  was 
abundant  everywhere,  but  in  1911  it  was  unusually  scarce.  The  year 
1910  seemed  to  be  the  summit  of  one  of  its  regular  periods  of  increase. 

HISTORY   OP   INTRODUCTION. 

In  the  autumn  of  1895  Dr.  L.  0.  Howard1  received  specimens  of  what 
later  proved  to  be  Scutellista  cyanea  Motsch,  from  Dr.  A.  Berlese  at 
Portici,  Italy.  These  were  bred  from  Ceroplastes  rusci  and  it  at  once 
occurred  to  Dr.  Howard  that  it  would  be  valuable  to  introduce  the  para- 
site into  this  country  to  prey  upon  Ceroplastes  floridensis,  an  injurious 
scale  in  our  southern  States.  It  was  not  until  1898  that  specimens  were 
received,  and  these  were  sent  to  Baton  Rouge,  Louisiana,  where  they 
were  distributed  by  Professor  H.  A.  Morgan,  as  well  as  in  the  Insectary 
at  Washington  by  Dr.  Howard  himself.  Both  of  these  introductions 
apparently  failed. 

A  year  later  Mr.  C.  P.  Lounsbury,  government  entomologist  of  Cape 
Colony,  found  this  species  parasitic  upon  Lecanium  olecB,  the  common 
black  scale,  and  sent  specimens  to  Washington  for  identification.  To 
quote  Dr.  Howard's  own  words2:  "The  past  spring  Mr.  Lounsbury,  at 
the  writer 's  request,  made  formally  through  the  United  States  Secretary 
of  Agriculture  to  the  Secretary  of  Agriculture  of  Cape  Colony,  brought 
with  him  from  Cape  Town  to  New  York  two  boxes  of  twigs  covered  with 
black  scale  affected  with  this  parasite,  and  expressed  them  to  Washing- 
ton, whence  they  were  immediately  forwarded  to  Mr.  E.  M.  Ehrhorn, 
the  horticultural  inspector  of  Santa  Clara  County,  California.  On 
June  19th  the  writer  received  a  letter  from  Mr.  Ehrhorn  announcing 
the  arrival  in  living  and  healthy  condition  of  the  parasites  in  question. 
The  twigs  in  one  box  were  somewhat  moldy,  but  quite  a  number  of 
parasites  were  crawling  about  in  the  box  and  were  found  in  the  pupal 
condition  in  some  of  the  scales.     Mr.  Ehrhorn  had  been  warned  by  tele- 


'Bull.   17,  U.   S.  Bur.  Ent.,  U.  S.  D.  A.,  p.   13. 
-Bull.  26,  U.  S.  Bur.  Ent.,  U.  S.  D.  A.,  p.   17. 

3— BUT,  223 


180  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 

graph  and  had  prepared  twenty-five  infested  oleander  plants  by  potting 
them  and  had  covered  each  with  a  bag  of  Swiss  muslin.  In  these  most 
of  the  parasites  were  liberated  and  a  few  allowed  to  fly  in  the  orchard. 
Specimens  of  a  hyperparasite  (Tetrastichus  sp.)  also  survived  the 
journey,  but  Mr.  Ehrhorn  was  on  the  lookout  for  this  parasite  and 
isolated  them  as  they  appeared,  pending  instructions  from  Washington 
as  to  their  destruction. ' ' 

Economic  Importance  and  Present  Status  in  California.  In  spite  of 
the  frequently  high  parasitization  by  Scutellista  the  black  scale  still 
remains  the  most  important  citrus  insect  pest  in  the  State.  While  the 
number  of  scales  may  be  considerably  reduced  through  the  work  of 
Scutellista,  the  standard  of  control  required  in  the  commercial  citrus 
orchard,  which  is  clean  fruit,  is  not  often  attained.  This  parasite  being 
an  egg-feeder,  it  does  not  affect  the  generation  of  scales  attacked.  These 
have  done  all  the  injury  they  would  otherwise  do,  even  though  they  had 
not  been  attacked  by  Scutellista;  unless  the  production  of  young,  and 
the  consequent  injury  by  them,  is  taken  into  consideration.  Many 
people  realize  that  the  parasite  is  present  and  doing  good  work  entirely 
on  the  basis  of  exit  holes  in  the  scales.  This  is,  of  course,  the  most  con- 
spicuous evidence,  and  does  tell  in  a  general  way  what  is  happening. 
But  the  real  test  of  what  this  parasite  is  accomplishing  is  to  be  found 
in  the  ability  to  prevent  young  from  appearing.  With  the  maximum 
number  of  exit  holes  there  may  still  be  an  abundance  of  young  settled 
on  the  leaves.  To  the  casual  observer  these  often  escape  notice  because 
they  are  inconspicuous.  That  this  number  of  young  frequently  runs 
high  may  be  indicated  by  the  fact  that  from  400  to  700  young  scales 
have  been  counted  on  each  of  the  leaves  arising  from  twigs  that  had 
75  per  cent  of  the  adult  scales  parasitized.  If  the  efficiency  of  the 
parasite  in  this  case  was  to  be  judged  solely  on  the  number  of  exit  holes 
it  would  have  been  pronounced  good,  when  as  a  matter  of  fact  it  was 
of  very  little  consequence.  It  might  be  said  that  there  would  have  been 
just  that  many  more  young  had  it  not  been  for  Scutellista;  but  in  this 
case  no  more  could  comfortably  settle  on  the  leaves.  To  follow  this  case 
further,  six  months  later  there  were  very  few  black  scales  on  the  tree. 
They  had  died  during  their  early  development,  a  good  many  before  the 
first  molt  and  many  more  before  the  second  molt.  If  the  young  had  not 
been  seen  on  the  tree  earlier  in  the  season  the  natural  inference,  con- 
cerning the  scarcity  of  the  young  scales  as  compared  with  the  adults, 
would  have  been  that  the  Scutellista  was  responsible. 

Such  an  instance  as  cited  has  been  observed  many  times.  And  the 
same  thing  happens  where  there  are  practically  no  Scutellista.  The  con- 
clusion is  forced  upon  us,  therefore,  that  other  factors,  aside  from  this 
parasite,  are  at  work,  and  even  though  the  parasite  be  present  in  large 


Bulletin  223]  THE  BLACK  SCALE.  181 

numbers,  it  does  not  necessarily  follow  that  it  keeps  the  scale  in  check. 
In  such  cases  as  mentioned  above,  the  scales  were  all  of  large  size,  and 
this  has  an  important  bearing  on  the  efficiency  of  Scutellista.  Where 
the  scales  are  small,  and  the  maximum  number  of  eggs  produced  may 
not  exceed  500,  the  Scutellista  consumes  them  all,  and  is  a  very  effective 
check  in  reducing  the  progeny.  On  the  other  hand,  where  from  2,500 
to  2,800  eggs  are  produced  there  are  more  than  are  necessary  to  bring 
the  Scutellista  larvse  to  maturity,  and  so  many  hatch  and  give  rise  to 
young  scales.  On  shade  and  ornamental  trees  the  degree  of  control 
effected  by  Scutellista  may  sometimes  be  sufficient,  but  this  standard  of 
control  is  much  less  likely  to  satisfy  the  exacting  demands  of  the  com- 
mercial citrus  grower.  But  even  on  such  shade  trees  as  the  pepper,  the 
infestation  often  becomes  so  severe  as  to  warrant  spraying,  as  was 
generally  done  in  the  city  of  Los  Angeles  during  the  past  year.  While 
the  Scutellista  should  have  full  credit  for  the  work  it  actually  does,  it 
should  not  be  counted  the  one  effective  agency  for  the  control  of  the 
scale  whenever  or  wherever  it  is  not  injurious.  In  Santa  Barbara 
County  practically  no  control  work  is  done  against  scale  insects  on 
citrus  trees.  In  many  places  in  the  county  the  black  scale  is  not 
injurious.  In  other  places  it  occurs  in  abundance,  and  there  is  much 
evidence  of  sooty  mold  fungus.  The  Scutellista  is  no  more  abundant 
there  than  elsewhere,  and  is  even  less  abundant  where  the  scales  are  not 
injurious.  So  it  is  in  smaller  sections  in  other  parts  of  the  citrus  belt. 
Distribution  of  Scutellista.  This  parasite  is  generally  distributed 
throughout  the  citrus  belt  of  southern  California.  It  may  occur  much 
more  abundantly  at  certain  times  in  some  groves  than  others,  but  if 
living  scales  are  present  and  in  the  proper  stage  Scutellista  will  soon 
be  found  infesting  them.  On  this  account  the  liberation  of  a  few  para- 
sites in  a  grove  will  not  greatly  augment  the  numbers  already  present. 
If  there  are  sections  that  happen  to  be  free  from  Scutellista,  then  arti- 
ficial introduction  will  greatly  aid  them  in  becoming  established.  In 
order  that  the  introduction  be  effective  they  should  be  liberated  at  a 
time  when  the  scales  are  in  the  proper  stage  or  shortly  before.  The 
best  season  for  this  will  be  during  May  and  June.  A  month  earlier  or  a 
month  later  will  also  find  scales  in  the  right  stage,  but  usually  in  fewer 
numbers.  Scales  will  be  found  somewhere  in  the  egg  stage  at  all  sea- 
sons, but  aside  from  the  months  mentioned,  examination  of  the  partic- 
ular grove  where  the  introduction  is  desired  should  first  be  made  to 
determine  the  condition  of  the  scale. 

DESCRIPTIONS — LIFE  HISTORY — HABITS. 

The  Egg.  The  egg  of  Scutellista  is  pearly  white  in  color,  oval,  more 
tapering  at  one  end,  from  which  arises  an  appendage  or  stalk.  The 
length  of  the  body  of  the  egg  is  about  .4  mm.  and  the  stalk  varies  from 


1H'2  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 

one  half  to  nearly  twice  that  length.  The  one  shown  in  the  figure  has 
a  stalk  of  the  extreme  length.  This  stalk  is  also  straighter  than  others, 
and  there  are  many  gradations  from  the  nearly  straight  one  shown  to 
those  having  a  sharp  double  curve.  The  eggs  are  found  beneath  the  scale 
either  among  the  eggs  of  the  scale  or  on  the  central  side  of  the  insect 
itself  if  the  eggs  are  not  yet  present.  Eggs  have  been  found  both  in  the 
field  and  insectary  under  scales  that  had  not  yet  reached  the  egg-laying 
stage.  Where  they  are  present  among  the  eggs  of  the  scale  they  can  be 
distinguished  from  the  latter  by  their  slightly  larger  size  and  lighter 
color.  The  duration  of  the  egg  stage  during  the  summer  months  is 
from  4  to  6  days. 

The  Larva.  The  young  larva  upon  hatching  from  the  egg  is  very 
much  like  the  mature  larva  excepting  that  it  is  smaller  in  size  and 
slightly  longer  in  proportion  to  the  width.  The  mature  larva  varies  in 
color  from  white  to  gray.  The  length  of  the  average  sized  specimens  is 
about  3  mm.  and  the  width  1  mm.  It  is  broadest  at  the  head  end  while 
there  is  a  gradual  tapering  toward  the  posterior  end.  The  body  consists 
of  14  segments.  The  head  segment  is  circular,  disc  shaped,  in  the  center 
of  which  is  the  mouth  opening.  The  external  mouth  parts  consists  of  a 
pair  of  sharp  chitinous  hooks  which  are  used  for  piercing  the  egg  shell, 
or  the  body  wall  of  the  scale  itself  if  eggs  are  not  present.  Above  and 
laterad  of  the  mouth  on  the  same  segment  is  a  pair  of  short  blunt  spines 
or  horns. 

The  young  larva  upon  hatching  soon  begins  to  feed  on  the  eggs  of  the 
scale  by  sucking  out  their  contents,  or  if  eggs  are  not  present  it  attacks 
the  scale  itself.  Several  instances  have  been  observed  where  the  larva 
had  grown  to  considerable  size  under  a  scale  that  had  not  yet  laid  eggs. 
It  is  not,  therefore,  strictly  an  egg  feeder,  as  generally  supposed,  but  of 
course  eggs  constitute  the  normal  food.  Larvae  have  been  reared  from 
the  soft  brown  scale  (C.  hesperidum)  in  which  case  no  eggs  at  all  were 
consumed,  for  this  scale  lays  no  eggs.  Larvae  have  also  been  seen  to  feed 
on  others  of  its  kind.  Cases  must  occur  in  nature  where  several  eggs  of 
the  parasite  are  deposited  under  the  same  scale,  but  one,  two,  sometimes 
three,  and  very  rarely  four,  come  to  maturity.  It  is  possible,  therefore, 
that  this  cannibalistic  habit  may  occur  more  or  less  frequently  in  nature. 

The  amount  of  food  consumed  or  the  number  of  eggs  necessary  to 
bring  the  larva  to  maturity  varies  greatly.  A  scale  has  not  yet  been 
found  too  small  to  have  a  Scutellista  pupa.  In  the  case  of  very  small 
scales  it  is  possible  that  the  larva  feeds  to  some  extent  on  the  scale  itself. 
Where  the  larva  appears  before  the  egg-laying  period,  its  attack  on  the 
scale  may  be  the  cause  of  the  scale  being  of  small  size,  or  of  causing  it 
to  deposit  eggs  before  it  is  fully  mature.  The  minimum  number  of  eggs 
laid  by  the  black  scale  may  be  as  low  as  200  while  counts  have  shown 
the  maximum  to  run  above  2,800.    The  size  of  the  mature  larva  will  vary 


Bulletin  223]  THE  BLACK  SCALE.  183 

greatly  in  these  two  cases  and  likewise  the  adult.  Where  the  smaller 
number  of  eggs  occur  they  are  all  consumed,  but  with  the  larger  num- 
bers more  than  enough  is  necessary  to  satisfy  the  larva,  and  consequently 
many  hatch. 

The  full  grown  larva  preliminary  to  pupation  hollows  out  a  cell  in 
the  old  egg  skins  and  mats  these  together  more  or  less  with  a  small 
amount  of  silk.  Strands  of  silk  are  frequently,  or  usually,  spun  from 
the  inner  edge  of  the  scale  to  the  twig,  thus  insuring  the  scale  remaining 
fixed  during  the  pupal  life  of  the  parasite.  It  has  been  frequently 
observed  that  old  scale  harboring  Scutellista  pupa  are  not  lifted  from 
the  twig  so  readily  as  those  not  parasitized.  Black  scale  that  have  thus 
been  parasitized  are  more  likely  to  remain  longer  on  the  tree  than  those 
that  are  not.  These  may  remain  on  the  tree  for  two  or  three  years  in 
many  parts  of  southern  California,  where  there  are  no  extremes  of 
weather  to  dislodge  them.  This  fact  is  not  often  taken  into  consideration 
in  estimating  the  amount  of  parasitization,  so  that  scales  with  exit  holes 
increase  with  each  year's  infestation,  while  those  without  are  more 
likely  to  drop  off. 

Length  of  Larval  Life.  A  larva  just  hatched  was  placed  in  a  capsule 
filled  with  eggs  of  the  scale  on  July  19th,  and  allowed  to  remain  until 
pupation,  which  occurred  on  the  15th  day.  Others  were  reared  under 
similar  conditions  and  the  larval  life  was  as  follows :  one  larva  16  days ; 
another  17  days;  another  20;  another  21 ;  and  another  17  days.  The 
larval  life  may  thus  vary  from  15  to  21  days,  with  an  average  of  about 
18  days. 

The  Pupa.  When  the  pupa  is  first  formed  it  is  white  in  color  like  that 
of  the  larva.  But  it  soon  begins  to  take  on  the  darker  color,  and  those 
under  observation  changed  to  the  jet  black  in  about  four  hours.  The 
scutellum,  eyes,  and  three  small  spots  on  front  of  head  were  first  to 
become  dark,  and  later  spots  appeared  on  the  abdomen.  In  two  hours 
the  whole  body  had  become  a  very  dark  gray,  tinged  in  spots  with  the 
characteristic  metallic  black.  At  this  time  the  parts  mentioned  above 
showed  blackest,  as  did  also  the  areas  where  the  wings  join  the  thorax, 
and  the  edges  of  the  abdominal  segments. 

The  length  of  the  pupa  varies  from  1J  to  3  mm.  The  large  scutellum 
is  conspicuous  and  extends  to  the  posterior  margin  of  the  second  abdom- 
inal segment.  The  sheaths  enclosing  the  wings,  legs  and  antennse  are 
plainly  visible  on  the  ventral  surface  and  the  whole  jet  black  in  color. 

Length  of  Pupal  Life.  On  June  24th  a  larva  pupated  and  was  iso- 
lated in  the  laboratory.  The  adult  emerged  in  18  days.  Others  in  the 
insectary,  where  conditions  were  nearly  like  out  of  doors,  showed  little 
variation.  The  following  records  were  obtained  at  different  times,  but 
all  during  the  summer  months:  3  females  in  pupal  stage  17   days; 


1  8  \  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION. 

3  females  18  days;  5  males  and  6  females  15  days;  8  females  16  days; 

2  females  17  days ;  2  males  17  days ;  1  female  16  days ;  1  female  19  days ; 

3  females  18  days;  1  male  and  2  females  19  days;  2  females  17  days; 
1  female  20  days.  The  minimum  is  thus  15  days  and  the  maximum  20 
days,  with  an  average  of  18  days  for  the  pupal  life. 

The  most  unusual  number  of  pupa  found  under  a  single  scale  is  one, 
but  two  are  commonly  found,  and  more  rarely  three,  while  four  have 
been  observed  twice  in  many  hundred  scales  lifted.  A  scale  with  four 
of  these  pupaa  is  shown  in  plate  V.  It  will  be  noticed  that  each  is  in  a 
separate  cell,  with  the  egg  skins  held  together  with  silk,  dividing  them. 

THE  ADULT  SCUTELLISTA. 

The  adult  is  the  familiar  hump-backed  blue  fly-like  insect  which  is 
often  seen  walking  slowly  about  among  the  scales.  It  is  strikingly 
different  from  any  of  the  other  Coccid  parasites.  The  scutellum  is  very 
long  and  extends  well  toward  the  tip  of  the  body.  The  head  is  broad, 
set  closely  into  the  thorax  and  is  bent  under,  forming  with  the  scutellum 
a  rounded  arch.  While  the  general  color  is  metallic  blue,  the  antenna? 
and  tarsi,  excepting  the  last  joint,  are  usually  light  brown. 

The  adult  upon  transforming  to  the  pupa  eats  out  a  circular  hole  in 
the  dorsal  surface  of  the  scale.  This  operation  of  eating  its  way  out  has 
occupied  from  one  to  three  hours  in  the  cases  that  were  kept  under 
observation.  They  are  in  the  adult  stage  from  one  to  three  days  before 
emerging.  This  has  been  determined  by  fastening  a  scale  to  a  cover 
glass  by  means  of  glue,  when  the  transformation  to  the  adult  could  be 
observed  and  the  time  of  emergence  noted.  In  lifting  scales  in  the  field 
it  will  be  noticed  that  occasionally  an  active  adult  makes  its  escape, 
though  no  exit  hole  has  been  started.  After  emerging  it  is  not  a  very 
active  flier  and  only  occasionally  indulges  in  extended  flights.  It 
crawls  about  actively  among  the  scales  and  when  disturbed  it  jumps  or 
flies  for  but  a  short  distance. 

Oviposition.  The  eggs  are  inserted  almost  invariably  under  the  arch 
at  the  posterior  tip.  The  ovipositor  is  thrust  forward  and  backward 
two  or  three  times,  the  egg  laid  and  ovipositor  withdrawn,  all  within 
about  one  half  minute.  The  position  of  the  insect  in  relation  to  the 
scale  is  just  opposite  that  of  A.  diaspidis  of  the  red  scale.  In  the  case 
of  the  latter  the  parasite  is  facing  away  from  the  scale,  and  the  ovi- 
positor is  inserted  by  a  pushing  backward.  With  Scutellista  the  insect 
is  facing  toward  the  center  of  the  scale,  and  the  ovipositor  is  inserted 
by  a  pulling  of  the  tip  of  the  abdomen  forward.  Scutellista  have  been 
observed  to  oviposit  within  twenty-four  hours  after  emerging.  It  does 
not  always  show  the  best  judgment  in  selecting  scales  for  oviposition. 
Oviposition  has  been  noted  to  occur  under  the  old  scales  from  which  all 
the  young  had  hatched;  also  under  scales  already  occupied  by  Scutellista 


Bulletin  223]  THE  BLACK  SCALE.  185 

larva ;  under  scales  where  not  enough  eggs  remained  to  bring  the  larva 
to  maturity,  and  where  the  young  had  hatched  but  died  before  emerging. 
Eggs  have  also  been  deposited  under  a  scale  where  there  was  a  larva  of 
Rhizobius. 

Several  eggs  may  sometimes  be  laid  under  the  same  scale,  but  this  is 
usually  done  by  different  individuals.  The  same  insect  will  lay  several 
eggs  in  succession,  but  different  scales  are  selected  for  each  deposition. 
In  the  laboratory  a  large  number  of  eggs  have  been  obtained  under  the 
same  scale.  Twenty  or  twenty-five  mature  females  were  confined  in  a 
test  tube  with  a  single  partly  grown  black  scale  and  more  than  fifty 
eggs  were  found  beneath  it  a  day  or  two  later.  So  many  were  deposited 
that  the  scale  was  lifted  from  the  twig.  In  such  a  case  they  were 
inserted  at  other  points  than  the  arch  at  the  posterior  end.  But  it  will 
be  noted  upon  consulting  plate  II  that  even  here  the  majority  were 
inserted  at  the  posterior  end.  Oviposition  has  been  noted  to  occur 
naturally  in  the  field  under  scales  that  had  not  yet  reached  the  egg- 
laying  stage.  In  the  insectary  the  youngest  scales  chosen  were  those 
that  had  recently  molted  the  second  time.  They  were  thus  mature,  but 
were  still  very  small  and  would  not  normally  deposit  eggs  for  several 
months  later.  But  this  was  under  forced  conditions,  and  such  young 
scales  would  probably  not  be  selected  in  the  field.  Young  scales  pre- 
vious to  the  second  molt  were  not  chosen  even  under  forced  conditions. 
About  50  female  Scutellista  were  confined  in  a  tube  enclosing  an 
oleander  leaf  on  which  were  black  scales  about  one  month  old.  A  day 
or  two  later  an  examination  of  the  scales  failed  to  reveal  any  eggs  having 
been  deposited.  On  a  check  experiment  with  mature  scales  eggs  were 
oviposited  under  freely. 

Proportion  of  the  Sexes.  In  a  considerable  number  of  specimens  col- 
lected at  different  times  the  number  of  males  and  females  do  not  vary 
greatly,  but  in  general  the  males  are  slightly  in  the  majority.  This 
seems  to  be  especially  true  where  the  scales  themselves  are  small.  The 
size  of  the  Scutellista  varies  greatly  and  this  is  dependent  upon  the  food 
supply.  The  males  are,  of  course,  smaller  than  the  females,  but  whether 
the  food  supply  has  any  influence  on  sex  determination  is  a  debatable 
subject,  with  the  greater  amount  of  more  recent  evidence  against  it. 

Parthenogenesis.  While  males  are  nearly  always  present  in  equal 
or  even  larger  numbers  than  females,  reproduction  is  apparently  able 
to  occur  without  the  males,  according  to  the  following  experiment. 
Mature  black  scales  with  eggs  were  allowed  to  remain  a  week  under 
cover  in  order  to  allow  any  chance  for  Scutellista  eggs  that  might  be 
present  to  hatch.  In  the  mean  time  several  pupae  were  put  each  in  a 
separate  box  and  the  adults  allowed  to  mature.  Two  of  these  unfertil- 
ized females  were  placed  in  a  vial  containing  a  twig  infested  with  a 
single  black  scale.     Seven  davs  later  the  scale  was  lifted  and  two  Scutel- 


186  UNIVERSITY   OP   CALIFORNIA EXPERIMENT   STATION. 

lista  eggs  and  four  larvae  were  found.  Since  the  eggs  hatch  in  from 
four  to  six  days  the  larvae  and  eggs  present  must  have  come  from  those 
liberated. 

Length  of  Adult  Life.  A  young  orange  tree  badly  infested  with  black 
scale  was  placed  in  a  screen  cage  and  several  Scutellista  of  both  sexes, 
which  had  just  emerged,  were  liberated.  The  conditions  were  as  nearly 
natural  as  possible,  there  being  ample  opportunity  for  oviposition,  or 
for  feeding,  if  necessary.  The  length  of  life  under  these  conditions  was 
10  to  15  days.  Others  which  had  recently  emerged  were  confined  in  pill 
boxes  without  food.  The  length  of  life  was  about  the  same  as  under  the 
above  conditions. 

By  spraying  sweetened  water  on  scale  infested  twigs  in  the  laboratory 
Mr.  P.  H.  Timberlake  and  Mr.  Rust  have  succeeded  in  keeping  the  adults 
alive  for  from  23  to  51  days. 

SEASONAL  HISTORY  OP  SCUTELLISTA. 

The  stages  and  abundance  of  Scutellista  are  very  much  dependent 
upon  the  same  conditions  in  its  host.  Since  the  black  scale  is  at  the 
height  of  egg  laying  in  June,  it  is  then  that  Scutellista  larva  will  be 
most  abundant.  The  pupal  period  follows  this  and  July  will  usually  be 
the  period  of  greatest  emergence  of  adults.  While  in  June  and  July 
the  various  stages  of  Scutellista  are  most  abundant,  it  will  be  found  to  a 
less  extent  in  all  stages  at  all  other  seasons.  Just  as  there  are  scales 
out  of  season  so  there  are  of  their  parasites.  But  during  the  off  season 
the  Scutellista,  like  the  scales,  may  not  be  found  in  the  same  grove. 
They  may  be  on  other  trees  than  citrus,  such  as  pepper,  olive,  or 
oleander,  or  they  may  be  on  citrus  trees  in  a  different  section,  or  even 
a  different  grove,  where  conditions  may  be  more  or  less  different. 

NUMBER  OF  GENERATIONS. 

Here  again  the  scale  determines  largely  the  number  of  generations. 
If  there  were  a  uniform  hatch  of  the  scale  occurring  during  the 
spring  and  no  more  scales  matured  until  the  same  time  next  year,  there 
would  be  but  one  generation  of  Scutellista.  Since,  however,  some  scales 
may  be  found  in  all  stages  at  all  seasons,  the  Scutellista  is  permitted  to 
go  through  several  generations.  The  number  will  thus  vary,  but  when 
the  scales  are  in  the  right  stage  the  number  can  be  calculated  from  the 
length  of  life  cycle.  One  record  from  egg  to  adult  will  indicate  the 
length  of  life  and  the  duration  of  the  different  stages. 

Egg  laid  July  22d ;  hatched  July  27th ;  pupated  August  12th ;  adult 
emerged  August  26th;  adult  died  September  4th.  The  egg  period 
is  thus  5  days,  larval  16,  pupal  15,  adult  9,  or  a  total  of  45  days  from 
the  egg  to  the  death  of  the  adult.  Another  completed  its  life  cycle  in 
43  days;  another  in  45  days;  another  in  50  days;  another  in  48  days; 


Bulletin  223] 


THE  BLACK   SCALE. 


18' 


another  in  44  days;  another  in  46  days,  and  another  in  50  days.  On 
this  basis  there  would  be  4  generations  from  May  to  October,  inclusive. 
From  November  to  April,  on  account  of  the  slower  development  during 
the  winter  months  there  will  be  from  2  to  3.  While  there  may  be 
thus  a  total  of  6  or  7  generations  a  year,  on  account  of  the  unfavorable 
condition  of  the  host,  4  or  5  will  be  nearer  the  actual  number. 


HYPERPARASITE. 

Cerchysius  sp. 
Under  the  old  black  scales  there  will  be  occasionally  found,  instead  of 
the  characteristic  Scutellista  pupa,  a  black  or  brown  oval  or  torpedo- 
shaped  body  that  may  at  first  be  mistaken  for  a  dipterous  puparium. 
This  will  be  found  to  be  the  old  larval  skin  of  the  Scutellista  larva  dis- 
tended and  harboring  a  parasite  within  this  parasite.  This  has  been 
taken  from  several  different  sections,  including  Whittier,  Glendale. 
Pomona,  Santa  Paula,  and  Santa  Barbara.  But  it  is  found  most  abund- 
antly at  Santa  Barbara,  where  in  certain  groves  the  percentage  of  Scu- 
tellista attacked  ran  between  5  and  10  per  cent. 

THE  LARVA. 

The  larva  of  this  hyperparasite  is  white  in  color,  length  2  mm., 
greatest  width  nearly  1  mm.,  13  segments,  broadest  at  head  end  and 


Fig.   12. — Hyperparasite  on  the  Scutellista,  Cerchysius  sp. 

gradually  tapering  toward  the  posterior.  Very  similar  in  color  and 
shape  to  that  of  its  host.  On  the  head  segment  of  the  larva  of  Scutellista 
there  is  present  above,  and  later  ad  of  the  mouth,  two  blunt  horns  or 
spines.  These  are  absent  on  the  larva  of  Cerchysius.  This  larva  com- 
pletely consumes  the  contents  of  the  Scutellista  larva,  leaving  only  the 
outside  epidermis.     This  is  changed  to  a  leathery  texture,  and  to  a  dark 


lsv  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

brown  or  black  color.  Preparatory  to  pupation  the  meconia  are  voided, 
and  these  are  to  be  found  compressed  into  one  end  of  the  larval  skin  of 
the  host.  Scutellista  larvae  attacked  by  its  parasite,  and  having  the  char- 
acteristic appearance  as  though  the  parasite  within  was  in  the  pupal 
stage,  were  collected  on  October  29th,  and  upon  removing  the  covering 
on  December  31st  the  hyperparasites  were  present  as  full  grown  healthy 
larva?.  From  this  it  would  appear  that  the  full  grown  larva  must  pass 
through  a  period  of  hibernation,  or  else  the  effect  on  the  host  is  made 
evident  very  early,  or  at  the  beginning  of  the  attack  by  the  parasite. 
Nearly  all  the  host  larvae  were  full  grown  when  they  took  on  the  char- 
acteristic appearance  of  parasitized  larvae,  but  a  few  have  been  taken 
when  they  were  but  one  half  grown.  Occasionally  the  host  manages  to 
change  at  least  partially  to  the  pupa.  In  such  cases  certain  characters 
of  the  pupa  appear,  as  the  constriction  at  the  head,  the  large  scutellum 
and  the  outline  of  the  abdomen,  but  there  are  practically  no  indications 
of  appendages  or  other  characters  of  the  true  pupa.  Specimens  from 
which  the  parasite  appeared  ready  to  emerge,  which  were  collected  in 
October,  were  still  in  the  larval  condition  in  January,  indicating  that 
the  winter  or  at  least  a  portion  of  the  winter  is  passed  as  a  full  grown 
larva. 

The  pupa  appears  to  change  within  its  old  larval  skin,  as  shown  in 
plate  VI.  This  was  removed  from  a  parasitized  Scutellista  larva  at  the 
same  time  that  the  full  grown  larvae  were  taken. 

THE  ADULT. 

Length  1§  mm. ;  wing  expanse  3  mm.  Head  and  thorax  finely  reticu- 
late and  covered  with  fine  black  hairs.  Entire  body  black,  with  greenish 
iridescence ;  front  leggs  entirely  black ;  middle  femur  with  band  of  light 
brown  at  proximal  one  third,  lighter  color  at  tip  of  femur,  and  greater 
area  at  tip  of  tibia ;  middle  tarsi  light  brown.  Hind  legs  entirely  black ; 
tibial  spurs  present,  middle  ones  largest.  Tarsi  5  jointed.  Antennae 
10  segmented,  pedicel  widened  in  center  and  twice  as  long  as  first  seg- 
ment; joint  3  equal  to  1,  remaining  joints  of  equal  length,  excepting  last. 
This  segment,  which  is  club-like,  is  divided  into  three  divisions.  The 
segments,  excepting  first  two,  are  covered  with  many  hairs  nearly  equal 
in  length  to  that  of  the  segment.  "Wings  not  fringed  or  with  very  short 
hairs.    Sub-marginal  vein  strong  and  with  row  of  conspicuous  spines. 

When  the  adult  is  ready  to  emerge  a  cap  or  portion  of  one  end  of  the 
larval  skin  of  the  Scutellista  is  broken  off  and  after  emerging  from  this 
eats  out  a  circular  hole  in  the  dorsum  of  the  scale  similar  to  the  Scutel- 
lista. excepting  that  they  appear  very  slightly  smaller  on  the  average. 


Bulletin  223] 


THE  BLACK   SCALE. 


189 


Tomocera   Californica   How. 

This  is  another  egg  parasite  of  the  black  scale,  and  formerly  was  as 
abundant  as  Scutellista  is  to-day.  In  1880  Professor  Comstock  stated 
that ' '  upon  more  than  one  tree  at  least  75  per  cent  of  the  scales  appeared 
to  be  parasitized.  In  no  locality  was  the  black  scale  found  without  this 
attendant  destroyer."  During  the  past  three  years  this  same  parasite 
has  been  but  occasionally  met  with.  So  scarce  has  it  been  that  we  have 
not  secured  enough  material  to  make  it  worth  while  undertaking  life 
history  studies.  It  seems  to  be  most  abundant  at  present  in  Santa 
Barbara  County  and  possibly  were  we  on  the  grounds  there  some 
material  might  have  been  available  for  life  history  work.  What  has 
changed  this  from  a  very  abundant  parasite  to  one  only  rarely  met  with 
is  difficult  to  account  for.  It  would  involve  a  thorough  study  of  the 
inter-relations  of  all  the  factors  bearing  on  the  subject.  Again,  some 
definite  and  specific  cause,  such  as  the  usurping  of  the  field  by  Scutel- 
lista,  might  account  for  it.  What  was  true  regarding  the  abundance  of 
Tomocera  in  1880  was  true  for  Scutellista  in  1910. 


DESCRIPTIONS  AND  LIFE  HISTORY. 

According  to  Comstock  the  female  pierces  the  body  of  the  scale  and 
deposits  probably  but  a  single  egg.    It  is  more  likely  that,  like  Scutel- 
lista, the  ovipositor  is  inserted  between  the  scale  and  the  twig.     The 
mature  black  scale,  with  its 
tough,    leathery    surface, 
would  not  be    easily  pene- 
trated by  the  ovipositor,  and 
it  might  also  result  in  injury  jS^^V^^^^ 
to  the  scale. 

The  larva  feeds  upon  the 
eggs  and  young,  and  to  some 
extent  on  the  scale  itself  if 
eggs  are  not  present.  When 
full  grown  it  is  about  4  mm. 
long,  broad,  spindle  shaped, 
somewhat  more  pointed  at 
the  anterior  than  the  poste- 
rior end  of  the  body.  Its 
color  is  clear  white,  the  contents  of  the  alimentary  canal  often  showing 
through,  giving  it  a  blackish  tinge.  This  larva  transforms  to  a  whitish 
pupa  which  soon  turns  black,  in  this  respect  again  being  similar  to 
Scutellista.  The  same  sort  of  an  exit  hole  and  of  the  same  size  is  made 
in  the  scale. 

The  adult,  in  general  color,  is  a  metallic  blue  black  insect.     Enough  of 


Fig. 


13. — Tomocera   californica   How. 
Report  U.  S.  D.  Agr.  for  1880. 


From 


190  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

Howard's  original  description1  is  given  herewith  to  enable  identification. 
Length  of  body  2.1  mm. ;  wing  expanse  3.5  mm. ;  abdomen  subovate,  first 
segment  large.  On  each  side  of  the  peduncle  on  the  anterior  part  of  the 
first  abdominal  segment  is  a  strong  tuft  of  snow  white  hairs.  Head, 
face,  scape  of  antennae,  and  under  side  of  all  legs,  light  mahogany 
brown.  Thorax  black  with  a  strong  metallic  luster  on  prothorax,  tip  of 
scutellum  and  scapulas,  abdomen  bluish  black  with  a  slight  brownish 
patch  beneath  at  the  base.  Tarsi  5  jointed.  The  center  of  the  forewing 
is  occupied  by  a  large  dusky  patch. 

Aphycus  Flavus  How. 

Aphycus  flavus  How.  is  parasitic  upon  the  male  black  scale.  Speci- 
mens of  this  parasite  have  been  taken  at  Whittier,  Glendale,  Pomona, 
and  San  Diego.  It  attacks  the  male  scale  in  the  second  stage  and  is 
strictly  an  internal  parasite.  It  also  attacks  the  female  at  about  the 
time  for  the  second  molt. 

The  larva  is  a  small,  white,  grub-like  creature,  measuring  when  full 
grown  about  1  mm.  long  and  \  mm.  broad.     It  is  the  broadest  near  the 


Fig.   14. — Aphycus  flavus  How.  parasite  of  soft  brown 
and  other  scales.     x40. 

head  end  and  tapers  gradually  toward  the  posterior "  end.  The  man- 
dibles are  very  broad  and  stout,  abruptly  tapering  into  a  sharp,  slightly 
curved  hook.  The  curved  tip  will  distinguish  it  from  the  larva  of 
A.  diaspidis. 

The  pupa  is  darker  in  color,  having  changed  from  the  white  color  of 
the  larva.  Its  length  is  8  mm.  and  greatest  width  J  mm.  The  eyes  are 
red. 

The  Adult.  Length  1.2  mm. ;  wing  expanse  2  mm. ;  color  dark  yellow, 
abdomen  darker;  eyes  reddish  black;  antennas  scape  with  dusky  patch 

XU.  S.  D.  A.  Report,  1880,  p.  368. 


Bulletin  223] 


THE  BLACK   SCALE. 


191 


above ;  wings  clear ;  veins  yellowish ;  antennae  11  jointed ;  pedicel  about 
twice  as  long  as  thick.     The  club  is  as  long  as  the  three  preceding  joints. 

OTHER  PARASITES. 

Aside  from  those  already  mentioned,  Coccophagus  lecanii  and  C. 
lunulatus  have  been  reared  from  the  partly  grown  scales.  But  all  of 
these  internal  parasites  are  very  scarce  as  compared  with  the  egg-feed- 
ing parasites. 

According  to  Mr.  C.  P.  Lounsbury,  the  following  parasites  have  been 
reared  from  the  black  scale  by  Mr.  C.  W.  Mally  in  South  Africa : 

Scutellista  cyanea  Motsch. 

Coccophagus  orientalis  How. 

Microterys  sp. 

Microterys  sp. 

Coccophagus,  near  ochraceus  How. 

Aphycus  lounsburyi  How. 

Tetrastichus  sp. 

Tetrastichus  sp. 

Coccophagus. 


1  >f.m 


Fig.   15. — Coccinellids  feeding  on  the  Black  Scale.     x5. 

1.  Olla  plagiata   Casey. 

2.  Axion   plagiatom   Casey. 

3.  Orcus  chalybeus  Boisd. 

4.  Larva,  pupa  and  adult  Rhizobius  ventralis   Black 


192  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 

PREDACEOUS  ENEMIES  OF  THE  BLACK  SCALE. 

Rhizobius  ventralis. 

The  commonest  and  most  characteristic  Coccinellid  attacking  the  black 
scale  is  Rhizobius  ventralis.  The  larva  feeds  on  the  eggs,  the  young  that 
have  not  emerged  from  beneath  the  parent,  and  the  younger  stages  of 
the  insect  after  it  has  settled.  On  account  of  its  firm  leathery  covering, 
the  adult  is  seldom  attacked  by  this  beetle. 

The  egg  is  pearly  white  in  color  and  oval  in  shape.  Its  length  is  .8  of 
a  millimeter  and  its  width  .4  mm.  They  are  found  under  the  scale. 
Plate  II,  figure  3  shows  five  such  eggs  in  their  natural  position  beneath 
the  black  scale.  Eggs  are  not  laid  here  exclusively,  for  this  beetle  feeds 
on  other  insects  than  the  black  scale.  And  sometimes  even  with  this 
scale  eggs  may  be  deposited  elsewhere,  but  they  are  very  commonly 
found  under  the  scale. 

The  Larva.  Length  5  mm. ;  width  1J  mm. ;  upper  surface  entirely 
black ;  prothorax  segment  surrounded  on  margins,  except  posterior,  with 
a  row  of  long  hairs,  those  laterally  arising  from  prominences.  A  row 
of  short  inconspicuous  hairs  on  either  side  of  the  dorsal  line,  two  hairs  in 
a  place,  papillae  scarcely  visible.  Another  row  slightly  more  than  one 
half  way  to  lateral  margin,  from  two  to  five  hairs  on  each  segment,  and 
arising  from  prominent  papillae.  Another  row  slightly  below  lateral 
margin  with  six  hairs  in  a  place  arising  from  very  conspicuous  pro- 
tuberances.    Ventral  surface  dirty  gray  with  legs  darker  in  color. 

The  larva  hatching  from  those  eggs  laid  under  the  scale  begin  to  feed 
on  the  scale,  or  the  eggs,  or  young.  In  case  the  scale  is  in  the  egg-laying 
stage  they  may  grow  to  considerable  size  under  the  same  scale,  and 
wander  about  attacking  many  different  scales.  It  is  in  this  stage  that 
the  most  feeding  is  done  and  consequently  is  most  efficient  as  an  enemy 
of  the  scale. 

The  Adult  is  broadly  oval  in  shape,  measuring  about  3  mm.  long. 
Thorax  and  elytra  shining  black  and  covered  with  gray  hairs.  The 
surface  is  finely  punctuate;  ventral  side  of  head  and  thorax  black. 
Abdomen  distinctly  brown.  Legs  black,  excepting  the  tarsi,  which  are 
brown. 


Bulletin  223]  THE  BLACK  SCALE. 

OTHER  PREDACEOUS  ENEMIES. 


193 


Orcus  chalybeus. 

This  is  the  steel  blue  beetle  that  is  found  commonly  on  citrus  trees, 
particularly  in  Santa  Barbara  County.  It  has  been  more  frequently 
met  with  on  black  scale  infested  trees  than  any  others. 

Several  other  species  of  Coccinellids  have  been  taken  from  black  scale 
infested  trees,  including  Hippodamia  convergens,  Coccinella  calif  ornica, 
Chilocorus  bivulnerus,  and  Axion  plagiatom. 


Fig.   16. — First  and  second  stages  of  some  unarmored  scale  insects. 

1  and  4.   Saissetia  oleae  Bern. 

2  and  5.  Coccus  hesperidum  Linn. 

3  and  6.  Lecanium  corni  Bouche. 


194 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


OTHER   SPECIES   OF  UNARMORED   SCALES   ASSOCIATED   WITH 

THE  BLACK  SCALE. 
Hemispherical  Scale. 

(Saissetia  hemisphmrica  Targ.) 

This  only  rarely  becomes  troublesome 
on  citrus  trees,  but  occurs  commonly  on 
ornamental  and  greenhouse  plants.  Its 
lighter  color,  glossy  surface,  smaller  size, 
and  the  absence  of  the  letter  H  will  read- 
ily distinguish  it  from  the  black  scale. 
The  common  parasites  are  Corny s  fusca 
and  Coccophagus  lecanii. 

Soft  Brown  Scale. 

(Coccus  hesperidum  Linn.) 
This  scale  frequently  attacks  citrus 
fruit  and  a  few  trees  or  parts  of  trees  are 
often  badly  infested.  Its  flatness  and 
lighter  color  distinguish  it  at  once  from 
the  black.  The  earlier  stages,  however, 
resemble  the  black  very  closely.  Some  of 
the  differences  are  shown  in  the  accom- 
panying figures.  Aplycus  flavus,  En- 
cyrtus  flavus,  Coccophagus  lecanii,  and  Coccophagus  lunulatus  are  the 
common  parasites  of  this  scale. 


Fig.   17. — Hemispherical  Scale 
on  twig  of  orange. 


Fig.   18. — Soft  brown  scales  with  exit  holes  of 
Aphycus  flavus. 


si    ^ 

Eh       ^^^(^^^jw            '    fi& 

'"  >4tNi 

iH  •   & 

"P 

1   f           '         t 

^ 

i 

r, »        *  ^ 

> 

1 

SjlWg>  J^W 

r     €1       -f^*^ 

^fc                              A 

. 

Plate  I. 

Photograph    of    small    orange    tree    in    the    field    showing    Black    Scale    on 

trunk  and  branches. 


Plate  II. 

1.  Different  stages  of  Black  Scale. 

2.  Young  Black  Scale  shortly  after  settling. 

?.   Eggs  of  Rhizobius  ventralis  under  Black  Scale.     xl7. 

4.  Hemispherical  scale  on  left  and  black  of  same  size  on  right. 

5.  Inverted  Black  Scale  with  50  eggs  of  Scutellista.     x30. 


Plate  ITT. 

1.  Black  scale  with  exit  holes  of  Scutellista. 

2.  Portion  of  same  more  enlarged. 

3.  Young  black  scale  hatched  but  died  before  emerging. 

4.  Eggs  and  young  scales  killed  by  fungus,  Isaria. 


Plate  IV. 

1.  Male  puparia  of  Black  Scale,     xl^. 

2.  Same  enlarged.     xl8. 

3.  Puparia  of  Hemispherical   Scale.     Same  magnification  as   2. 


Plate  V. 
Scutellista    cyanea    Motsch,    egg    x70  ;    larva    x25  ;    pupae,    ventral    and    dorsal 
views  x20  ;  adult  xl7  ;  inverted  Black  Scale  showing  four  pupae;  exit  holes 
in  scales. 


Plate  VI. 
Larva  of  Scutellista  parasite,  Cerchysius  sp.     x25. 
Larva  of  Cerchysius  partly  changed  to  pupa.     x25. 
Parasitized  larva  of  Scutellista  harboring  Cerchysius  within.     x25. 
Appearance  of  parasitized  Scutellista  larva  beneath  scale.     x25. 
Normal  Scutellista  pupa.     x20. 
Parasitized   Scutellista  pupa  or   Scutellista  larva  which   succeeded   in  partly 

changing  to  pupa.     x20. 
Exit  hole  of  parasite  in  old  larval  skin  of  Scutellista. 
Black  scale  killed  by  fungus,  Isaria. 
Fungus  covering  scale  and  spreading  over  twig. 


Plate  VII. 
Photomicrographs  of  derm  pores.     x50. 

1.  Saissetia  oleae  Bern. 

2.  Saissetia  hemisphaerica  Targ\ 

3.  Lecanium  corni   Bouche. 

4.  Lecanium  pruinosum  Craw. 

5.  Lecanium  sp.  on  Heteromeles. 

6.  Coccus  hesperidum  Linn. 


Leaf  on   right   showing  sooty  mold  fungus  as  a  result  of  Black   Scale   infes- 
tation.    Normal  leaf  on  left. 


Saissetia  olese  on  Olive. 
Plate  VIII. 


Bulletin  223] 


THE  BLACK   SCALE. 


195 


^tf/rtMw*11'. 


^-m--m^ 


■'^.;-'-st    ^w 


•    ■ . 


Fig.   19. — Encyrtus  flavus  How.       9    x25- 
European  Fruit  Lecanium. 
{Lecanium  corni  Bouche.) 
This  is  what  has  been  called  the  brown  apricot  scale  in  this  State  and 
went  by  the  scientific  name  of  Eulecanium  armeniacum  Craw.     Pro- 
fessor J.  G.  Sanders1  in  a  recent  study  of  the  Lecanium  group  places  it 


c V*i 


^r# 


Fig.   20. — Coccophagus  lunulatus  How.,   parasite   of  soft  brown  and 
other  scales. 

under  the  name  given  above.  This  scale  does  not  occur  on  citrus  trees, 
so  far  as  we  have  seen,  but  is  frequently  associated  with  the  black  on 
prune,  apricot  and  other  deciduous  trees.  Comys  fusca  is  the  com- 
monest parasite  and  is  widely  distributed. 


aJour.  Ec.  Ent.,  vol.  2,  No.  6.  p.  443. 


4— bul.  223 


196 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


c^fe 


Fig.   21. — Antennae  and  anal  lobes. 

1.  Saissetia  oleae  Bern. 

2.  Lecanium  pruinosum  Coq. 

3.  Coccus  hesperidum  Linn. 

4.  Lecanium  corni  Bouche. 

The  Frosted  Scale. 
(Lecanium  pruinosum  Coq.) 
This  scale  is  very  similar  to  L.  corni  and  frequently  occurs  with  it 
as  well  as  with  the  black.  It  is  usually  considerably  larger  than  corni 
and  is  covered  with  pruinose,  hence  the  name.  In  southern  California 
it  not  infrequently  occurs  on  the  English  walnut.  Comys  fusca  has  also 
been  reared  from  this  scale. 


Lecanium  sp. 
This  scale  occurs  very  commonly  on  the  Christmas  berry  Heteromeles. 
It  was  at  first  mistaken  for  the  Hemispherical  scale,  but  typical  speci- 
mens appear  much  larger  and  slightly  different  in  shape.    Upon  drying 
they  are  also  inclined  to  shrivel,  as  indicated  in  the  figure.     It  is  very 


Bulletin  223] 


THE  BLACK    SCALE. 


197 


Fig.   22. — Lecanium  sp.  on  Heteromeles. 


Fig.   23. — Comys  fusca  How.,  parasite  on  Hemispherical,  Brown  Apricot, 
and  other  scales.     x!8. 


19S 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


heavily  parasitized  by  Comys  fusca  and  to  a  less  extent  by  Coccophagus 
lecanii.  The  former  attacks  only  the  larger  scales,  and  since  these  come 
to  maturity  in  May  and  June  this  is  the  time  when  most  of  the  parasites 
emerge.  Scales  attacked  by  C.  fusca  do  not  lay  eggs.  While  C.  lecanii 
usually  attack  the  smaller  scales,  not  infrequently  the  larger  ones  are 
also  chosen.  One  or  two  of  these  parasites  may  mature  in  the  scale  and 
yet  eggs  will  be  deposited  by  the  scale. 


Fig.  24.- 


-1.   Larva  of  Comys  fusca.     2.  Pupa  of  Comys  fusca. 
3.   Pupa  of  Coccophagus  lunulatus. 


SYSTEMATIC  POSITION  AND  RELATIONSHIPS. 

Saissetia  oleae  Bern,  belongs  to  the  subfamily  Coccince,  of  the  family 
Coccidce,  which  is  characterized  by  the  possession  of  triangular  supra- 
anal  plates.  This  species  is  readily  recognized  by  a  median  longitudinal 
carina  and  two  transverse  carinas  forming  the  characteristic  H.  Other 
species  of  the  genus  recorded  from  California  are :  filicum  Bvd.,  hemis- 
phcerica  Targ.,  and  nigra  Mitn.  Aside  from  hemisphcerica  these  species 
are  limited  to  a  greenhouse  locality  and  are  of  no  particular  importance. 
The  species  olece  was  first  described  under  the  genus  Chermes.  A  few 
years  later  it  was  placed  under  the  genus  Coccus.  In  1852  the  name 
Lecanium.  was  given  for  the  genus  and  for  a  long  while  it  was  thus 
known  by  various  writers  until  it  was  changed  by  Professor  Cockerell  to 
Saissetia  in  1901. 


Bulletin  223]  THE  BLACK  SCALE.  199 


BIBLIOGRAPHY. 

Up  to  1903,  the  bibliography  of  Saissetia  oleae  is  given  in  Fernald's 
Coccidae  of  the  "World.  The  following  includes  the  references  to  this 
insect  since  1903,  which  has  been  furnished  through  the  courtesy  of 
Mr.  E.  R.  Saccer,  of  the  Bureau  of  Entomology,  Washington. 

Saisettia  oleae  Bern. 

Reh,  Dr.  L.  :  Zeitschr.  f.  Eutom.  VIII,  pp.  418-419.     Nov.  1,  1903. 
Bibliography,  food  plants,   etc. 

Theobald,  F.  V.  :  1st  Rept.  Ec.  Ent.  Br.  Mus..  p.  140  (1903). 

Coleman.  G.  A.  :  Journ.  N.  Y.  Ent.  Soc.  XI,  p.  82.     June,  1903. 

Coleman,  G.  A.  :  Journ.  N.  Y.  Ent.  Soc.  XI,  p.  74.     June,  1903. 

King.  G.  B.  :  Ent.  News,  XIV,  p.  205.     June,  1903. 

Thro.   W.  C.  :   Bull.  209.     Cornell   Univ.   Agr.  Exp.   St.,   p.   214,  pi.   IV ;   figs.   1-3 ; 
pi.  V,  fig.  8,  Jan.  1903. 

Ehrhorn.  E.  M. :  1st  Bien.  Rept.  of  Com.  Hort.  Sta.  Cal.     1903-04.     p.  111. 

Stiftz,  A.:  Jahr.  d.  Pflanz.      (1904.)     p.  137. 

Kirkaldy,  G.  W.  :  The  Entomologist,  vol.  XXXVII,  Sept.  1904,  p.  228. 

Green.  E.  E. :  The  Coccidae  of  Ceylon.     Part  III,  p.  227   (1904). 

On  Antidesma  bunius,  Grewia  orientalis,  Duranta,  Thespesia  populnea,  Cajanus 
indicus. 

Dickel.  Dr.  O.  :  Zeit.  f.  wiss.  Insekt.  Heft  II.     Bd.  I,  Nov.  20,  1905,  p.  447. 

Simpson,  C.  B. :  Transvaal  Dept.  Agric.  Ann.  Rept.  of  Director.     1904-1905,  p.  350. 

Cockerell,  T.  D.  A. :  Proc.  Davenport  Acad.  Sciences,  vol.  X,  1905. 

Del  Guercio  :  Boll.  Uff.  del  Min.  d'Agr.  Indust.  &  Comm.     V.  3,  p.  262  (1906). 

Records  Tomocera  californica,  Coccophagus  sp.  and  Scutellista  cyanea  as  para- 
sites. 

Tyrrell,  Mary  W.  :  Rep.  Agr.  Exp.   Sta.  of  the  Univ.  Cal.     Year  1894-'95,  p.  265. 
Plates  II,  III,  IV. 

Herrera,  A.  L. :  Bol.  d.  1.  Com.  de  Parasitologia  Agric.     Tomo  III.     num.  I   (1906). 

Ehrhorn,  E.  M.  :  The  Can.  Entom.    Vol.  XXXVIII.  No.  10,  Oct.  1906,  p.  332. 

Gahan,  A.  B. :  Bull.  119  Mel.  Ag.  Exp.  Sta.    July,  1907,  pp.  11-12,  fig.  4. 

Ehrhorn.  E.  M.  :  2d  Bien.  Rep.  Com.  of  Hort.  Sta.  of  Cal.    1905-'06.     pp.  23  and  223. 

Carnes,  E.  K. :  2d  Bien.  Rep.  Com.  Hort.  Sta.  Cal.     1905-'06  (1907),  pp.  193-194. 

Paoli.  Berlese  An.  &  Am.:  "Redia,"  vol.  IV,  Fasc.  I,  pp.  48-80.     4  figs.     (07.) 

Figures  illustrating  various  stages  of  L.  oleae,  as  well  as  those  of  its  predaceous 
and  parasitic  enemies. 

Green.  E.  E. :  Trans.  Linn.  Soc.  of  London.     Vol.  XII,  part  2,  Dec.  1907,  p.  200. 

Reported  from  Chagos  Is.,  Aldabia,  Mauritius,  Europe,  N.  Z.,  Australia,  China, 
Japan,  Java,  H.  I.,  S.  Africa,  Ceylon,  Brazil,  W.  Indies,  Mexico,  U.  S.  A. 

Newman.  L.  J.  :  Jn.  Dep.  Ag.  of  Western  Australia.     Vol.  XV,  part  12.     Dec.  1907. 
p.  914. 
"Reduced  to  a  harmless  scale  in  this  state  by  its  introduced  natural  enemies." 

Froggatt,  W.  W. :  "Australian  Insects"   (1907),  p.  370. 

Autran,  E.  :  Bol.  del  Min.  di  Agr.     Vol.  VII,  No.  8,  p.  151,  1907. 

Howard,  C.  W. :  Transvaal  Ag.  Jn.     Vol.  VI,  No.  22,  Jan.  1908,  p.  274. 

Froggatt,  W.  W. :  The  Jn.  of  Agr.  of  Victoria.    Vol.  VI,  pt.  5,  8th  May,  1908,  p.  277. 

Lea,  A.  :  Insect  and  Fungus  Pest  of  Orchard  and  Farm.  Tasmania,  3d  edition,  p.  64. 
(1908.) 

Pease,  S.  A.:  34th  Fruit  Growers'  Convention  Sta.  of  Cal.     (1908.)     p.  40. 

Lounsbury.  C.  P.  :  Rep.  of  Gov.  Ent.     Year  1907.     Cape  of  Good  Hope,  Dep.  Agr. 
Cape  Town.     1908. 

Cook,  A.  J.  :  Off.  Rep.  34th  Fruit  Grow.  Con.  of  Cal.     p.  50.     Sacramento.     1908. 

Ehrhorn.  E.  M.  :  Proc.  of  33d  Fruit  Grow.  Con.  of  Cal.     p.  151.     (190S.) 


200  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 

Cook,  M.  T. :  Bull.  No.  9.     Estacion  Central  Agron.  de  Cuba.     Feb.  190S.     p.  26. 

fig.  34. 
Froggatt,  W.  W.  :  The  Jn.  Dept.  of  Ag.  of  So.  Australia.     Vol.  XII,  No.  1,  Aug. 

1908.     p.  38. 
Martinelli,   Dr.    G.  :    Bol.    di    Lab.    di   Zool.    Generale    e    Agraria.      Vol.    II    (1908) 

pp.  217-20. 
Descr.  fig.  hosts  and  parasites. 
Newman,  L.  J. :  Jn.  Dept.  of  Ag.  W.  Australia.     Dec.  1908.     Vol.  XVII,  p.  942. 
Cook,  M.  T.,   &  Home,   W.  T. :   Bull.   No.   9.     Estacion   Central   Agron.   de   Cuba. 

Feb.  1908.    p.  26.    fig.  34. 
Lindinger,  L.  :  Zeit,  f.  wiss.  Insektenbiol.,  v.  5,  p.  224   (1909). 

Essig,  O.  E. :  Pomona  Jn.  of  Entom.    Vol.  1,    No.  1.     March,  1909.     pp.  12-15.    fig.  9. 
Carnes,  E.  K. :  3d  Bien.  Kept.  Com.  Hort.  Cal.     p.  25.      (1909.) 
Dean,  Geo.  A. :  Trans.  Kans.  Acad,  of  Sciences.    Vol.  XXII.     p.  269.     (1909.) 
Sanders,  J.  G.  :  Jn.  Econ.  Ent.     Vol.  II.     No.  6.     p.  440.     pi.  20.     fig.  2.     Dec.  1909. 
Severin,  H.  C,  &  H.  H.  P. :  Jn.  Econ.  Ent.     Vol.  II.     No.  4.    p.  297.    Aug.  1909. 
Newman,  L.  J.  :  Jn.  Dept.  Agr.  W.  A.     XVIII,  7,  p.  500  (1909).     Fig. 
Fullaway,  D.  T.  :  Hawaii  Agr.  Exp.  Sta.  Bui.  18.     p.  16.      (1909.) 
Pestana,  C. :  Bull.  Agricole  de  PAlgierie  et  de  la  Tunisie,  No.  6,  15,  March,  1909. 

pp.  146-48. 
Brick,  C. :  Sta.  fur  Pflanzenschutz  zu  Hamburg,  X,  p.  11.     (1909.) 
Garcia,  N. :  Bol.  Agr.  Tech.  y  Econ.  1,  No.  3,  p.  268.     (1909.) 
Brick,  C.  :  Sta.  fur  Pflanzenschutz  zu  Hamburg,  XI,  p.  6.     (1909.) 
Kirk,  T.  W.,  &  Cockayne,  A.  H. :  Ann.  Rep.  Dept.  Agr.  Div.  Biol.  &  Hort.     p.  285. 

(1909.) 
Doane,  W.  R. :  Can.  Ent,  xli,  8,  p.  297.     (1909.) 
Barber,  T.  C. :  Jn.  Econ.  Entom.     Vol.  3,  No.  5,  p.  424.     Oct.  1910. 
Knischewky:  Zeit.  fur  Pflanzenkrankheiten,  Band  XX,  Heft.  5,  p.  267.     (1910.) 


STATION     PUBLICATIONS    AVAILABLE    FOR     DISTRIBUTION. 


REPORTS. 

1896.  Report  of  the  Viticultural  Work  during  the  seasons  1887-93,  with  data  regard- 

ing the  Vintages  of  1894-95. 

1897.  Resistant  Vines,  their  Selection,  Adaptation,  and  Grafting.      Appendix  to  Viti- 

cultural Report  for  1896. 

1902.  Report  of  the  Agricultural  Experiment  Station  for  1898-1901. 

1903.  Report  of  the  Agricultural  Experiment  Station  for  1901-03. 

1904.  Twenty-second  Report  of  the  Agricultural  Experiment  Station  for  1903-04. 


BULLETINS. 


Reprint. 

No.    128. 

133. 

147. 
149. 
151. 
152. 
153. 
159. 

162. 

165. 

167. 

168. 

169. 

170. 
171. 

172. 

174. 
176. 

177. 

178. 
179. 

180. 
181. 
182. 


183. 

184. 


185. 


186. 
187. 


188. 
189. 


Endurance  of  Drought  in  Soils  of  I  No. 

the  Arid  Region. 
Nature,  Value,  and  Utilization  of  I 

Alkali  Lands,  and  Tolerance  of  j 

Alkali.      (Revised  and  Reprint,  i 

1905.) 
Tolerance    of   Alkali    by   Various  j 

Cultures. 
Culture  Work  of  the  Sub-stations,  j 
California  Sugar  Industry. 
Arsenical  Insecticides. 
Fumigation  Dosage. 
Spraying  with  Distillates. 
Contribution     to     the     Study     of 

Fermentation. 
Commercial  Fertilizers.      (Dec.  1,  j 

1904.) 
Asparagus    and    Asparagus    Rust 

in  California. 
Manufacture    of    Dry    Wines    in 

Hot  Countries. 
Observations  on  Some  Vine  Dis-  j 

eases  in  Sonoma  County. 
Tolerance  of  the  Sugar  Beet  for  j 

Alkali. 
Studies  in  Grasshopper  Control. 
Commercial     Fertilizers.        (June 

30,  1905.) 
Further  Experience  in  Asparagus 

Rust  Control. 
A  New  Wine-cooling  Machine. 
Sugar  Beets  in  the   San  Joaquin 

Valley. 
A   New    Method    of   Making   Dry 

Red  Wine. 
Mosquito  Control. 
Commercial    Fertilizers.       (June, 

1906.) 
Resistant  Vineyards. 
The  Selection  of  Seed- Wheat. 
Analysis     of     Paris     Green     and 

Lead    Arsenic.       Proposed    In- 
secticide Law. 
The  California  Tussock-moth. 
Report   of   the   Plant   Pathologist 

to  July   1,   1906. 
Report  of  Progress  in  Cereal  In- 
vestigations. 
The  Oidium  of  the  Vine. 
Commercial    Fertilizers.       (Janu- 
ary,  1907.) 
Lining  of  Ditches  and  Reservoirs 

to  Prevent  Seepage  and  Losses. 
Commercial    Fertilizers.       (June, 

1907.) 


190.  The  Brown  Rot  of  the  Lemon. 

191.  California  Peach  Blight. 

192.  Insects  Injurious  to   the  Vine   in 

California. 

193.  The  Best  Wine  Grapes  for  Cali- 

fornia ;  Pruning  Young  Vines  ; 
Pruning  the  Sultanina. 

194.  Commercial     Fertilizers.        (Dec, 

1907.) 

195.  The  California  Grape  Root- worm. 

197.  Grape  Culture  in  California  ;    Im- 

proved Methods  of  Wine-mak- 
ing; Yeast  from  California 
Grapes. 

198.  The  Grape  Leaf -Hopper. 

199.  Bovine  Tuberculosis. 

200.  Gum  Diseases  of  Citrus  Trees  in 

California. 

201.  Commercial    Fertilizers.       (June, 

1908.) 

202.  Commercial  Fertilizers.      (Decem- 

ber, 1908.) 

203.  Report   of   the   Plant  Pathologist 

to  July  1,  1909. 

204.  The  Dairy  Cow's  Record  and  the 

Stable. 

205.  Commercial  Fertilizers.      (Decem- 

ber,   1909.) 

206.  Commercial    Fertilizers.       (June, 

1910.) 

207.  The  Control  of  the  Argentine  Ant. 

208.  The  Late  Blight  of  Celery. 

209.  The  Cream  Supply. 

210.  Imperial     Valley     Settlers'     Crop 

Manual. 

211.  How    to    Increase    the    Yield    of 

Wheat  in  California. 

212.  California  White  Wheats. 

213.  The  Principles  of  Wine-making. 

214.  Citrus  Fruit  Insects. 

215.  The  House  Fly  in  its  Relation  to 

Public  Health. 

216.  A  Progress  Report  upon  Soil  and 

Climatic  Factors  Influencing 
the  Composition  of  Wheat. 

217.  Honey  Plants  of  California. 

218.  California  Plant   Diseases. 

219.  Report  of  Live   Stock  Conditions 

in  Imperial  County,  California. 

220.  Fumigation  Studies  No.   5  ;    Dos- 

age Tables. 

221.  Commercial    Fertilizers.       (Octo- 

ber,   1911.) 

222.  The  Red  or  Orange  Scale. 


CIRCULARS. 


No.      1.   Texas  Fever. 

5.   Contagious  Abortion  in  Cows. 
Remedies  for  Insects. 
Asparagus  Rust. 
Fumigation  Practice. 
Silk  Culture. 

Recent    Problems    in    Agriculture. 
What  a  University  Farm  is  For. 
Disinfection  of  Stables. 
Preliminary    Announcement    Con- 
cerning Instruction  in  Practical 
Agriculture  upon  the  University 
Farm,  Davis,  Cal. 
30.  White  Fly  in  California. 

32.  White  Fly  Eradication. 

33.  Packing    Prunes    in    Cans.      Cane 
Sugar  vs.  Beet  Sugar. 

Analyses  of  Fertilizers  for  Con- 
sumers. 

Instruction  in  Practical  Agricul- 
ture at  the  University  Farm. 

Suggestions  for  Garden  Work  in 
California  Schools. 

Butter  Scoring  Contest,  1909. 

Insecticides. 

Fumigation  Scheduling. 


7. 

9. 

11. 

12. 

15. 

19. 

2  9. 


36. 
39. 

4  6. 

48. 

19. 
50. 


No.   52.  Information  for  Students  Concern- 
ing the  College  of  Agriculture. 

54.  Some      Creamery     Problems     and 

Tests. 

55.  Farmers'    Institutes    and    Univer- 

sity Extension  in  Agriculture. 

58.  Experiments  with  Plants  and  Soils 

in  Laboratory,  Garden,  and  Field. 

59.  Tree  Growing  in  the  Public  Schools. 

60.  Butter  Scoring  Contest,  1910. 

61.  University  Farm  School. 

62.  The  School  Garden  in  the  Course 

of  Study. 

63.  How  to  Make  an  Observation  Hive. 

64.  Announcement   of  Farmers'    Short 

Courses  for  1911. 

65.  The  California  Insecticide  Law. 

66.  Insecticides  and  Insect  Control. 

67.  Development  of  Secondary  School 

Agriculture  in  California. 

68.  The  Prevention  of  Hog  Cholera. 

69.  The    Extermination    of    Morning- 

Glory. 

70.  Observations     on     the     Status     of 

Corn  Growing  in  California 


